Frankenstein authorship question

The "Frankenstein" authorship question refers to the historical uncertainty that exists around Percy Bysshe Shelley's contributions to 
"Frankenstein; or, The Modern Prometheus", a novel attributed to Shelley's wife, Mary Shelley.
Author Duncan Wu claims the uncertainty ended with the publication of transcribed manuscripts in 1996 which he says make it evident that Mary Shelley was the creative force behind the work, while Percy Shelley provided contributions which were editorial in nature. This is the "handwriting argument" that maintains that everything in Mary's handwriting was written by her, even though letters by her show that Percy Bysshe Shelley dictated portions of the novel. Moreover, the last 15 galley proof pages of the novel were in his handwriting. In other words, he wrote the ending to the novel as opposed to merely editing or correcting grammar. The handwriting argument has been challenged as overly simplistic and misleading. Advocates who continue to maintain that Percy Shelley had a much greater role – even the majority role – in the creation of the text have been dismissed by some mainstream scholars.
Background.
The dispute over authorship began as soon as the novel was published anonymously on January 1, 1818 in London. There was much speculation and controversy over the actual author of the book. Percy Bysshe Shelley was suspected as the author but he denied any role whatsoever in the writing of the book. He claimed that he only supervised the manuscript during its publication.
The novel was first attributed to Percy Bysshe Shelley in an 1818 review by Walter Scott who recognized Shelley's style and ideas in the Preface and noticed Shelley's poem "Mutability" and poetry passages and citations in the book. Percy Shelley had written the Preface "Mutability". He also selected poetry passages such as the John Milton epigraph. However, these facts were not known at the time. Scott concluded that it was "an extraordinary tale, in which the author seems to us to disclose uncommon powers of poetic imagination".
The next public challenge to Mary Shelley's authorship came in 1824. She had written a follow-up novel that was reviewed in Charles Knight's literary magazine called "Knight's Quarterly Review". In the section titled "Frankenstein", the reviewer alleged that the follow-up novel and Frankenstein were written by two different authors:
"[T]here is not the slightest trace of the same hand -- instead of the rapidity and enthusiastic energy which hurries you forward in "Frankenstein", every thing is cold, crude, inconsecutive, and wearisome; -- not one flash of imagination, not one spark of passion -- opening it as I did, with eager expectation, it must indeed have been bad for me after toiling a week to send the book back without having finished the first volume. This induced me to read "Frankenstein" again -- for I thought I must have been strangely mistaken in my original judgment. So far, however, from this, a second reading has confirmed it. I think "Frankenstein" possesses extreme power, and displays capabilities such as I did hope would have produced far different things from Castruccio. ... But whence arises the extreme inferiority of "Valperga"? I can account for it only by supposing that Shelley wrote the first, though it was attributed to his wife, -- and that she really wrote the last. … It has much of his poetry and vigour … At all events, the difference of the two books is very remarkable." 
An author for the novel was first given in the 1821 second overall edition: The French translation was published in Paris by Aléxandre Corréard as "Frankenstein, ou le Prométhée moderne" by Jules Saladin with the author attributed as being "M.me Shelly". The second (English) edition was published two years later in 1823. It was published in London by G. and W.B. Whittaker. The publication came under the supervision of William Godwin, who is Mary Shelley's father. Godwin listed the author as "Mary Wollstonecraft Shelley". He made "114 substantive changes" to the 1818 edition. He decided to not credit Percy Bysshe Shelley as the author of the Preface. Godwin also did not cite Percy Shelley as the author of the poem "Mutability" which gave implications that Mary Shelley was the author of the poem. He also removed the John Milton epigraph from Paradise Lost. Godwin failed to credit Percy Shelly for his textual contributions.
In the 1831 edition published by Henry Colburn and Richard Bentley in London, Mary acknowledged for the first time that Percy Bysshe Shelley wrote the preface. This third edition was a heavily revised version of the 1818 original that significantly and substantially altered the novel.
The authorship issue was revived in 1974 when drafts and proofs of the novel revealed that some sections were written in Percy Bysshe Shelley's handwriting. James Rieger, an English professor and editor, in a publication of the original 1818 edition in 1974, republished in 1982, argued that Shelley made significant contributions to the novel and should be regarded at least as a "minor collaborator" or even as a collaborator: "His assistance at every point in the book's manufacture was so extensive that one hardly knows whether to regard him as editor or minor collaborator. ... Percy Bysshe Shelley worked on "Frankenstein" at every stage, from the earliest drafts through the printer's proofs, with Mary's final 'carte blanche to make what alterations you please.' ... We know that he was more than an editor. Should we grant him the status of minor collaborator?" He claimed that Shelley was intricately and minutely involved in the composition of the novel from the outset.
English professor Charles E. Robinson placed Shelley's name on a 2008 edition of the book "The Original Frankenstein" which caused widespread media comment and discussion. In 2015, in "The Neglected Shelley", Robinson examined Shelley's alleged significant contributions to the novel in greater detail.
Chronology.
Authors have examined and investigated Percy Bysshe Shelley's scientific knowledge and experimentation, his two Gothic horror novels published in 1810 and 1811, his atheistic worldview, his antipathy to church and state, his 1818 Preface to "Frankenstein", and his connection to the secret anti-Catholic organization, the Illuminati. These revelations showed that the novel drew inspiration from Shelley's life, background, his readings such as John Milton's "Paradise Lost", "Ruins of Empires" (1791) by Constantin François de Chassebœuf, comte de Volney, which also informed "Ozymandias", also published in 1818, Sir Humphry Davy's "Elements of Chemical Philosophy" (1812), a textbook which Percy Bysshe Shelley owned, and the works of Dr. Erasmus Darwin, the grandfather of Charles Darwin, whom Shelley had earlier cited as a major influence in "Queen Mab" (1813), his views on religion, his poetic style, and his themes and ideas. In letters to William Godwin, Shelley also mentioned his affinity for Paracelsus, Albertus Magnus, and Heinrich Agrippa, "some of the physiological writers of Germany" cited in his 1818 Preface to "Frankenstein". Based on its science, style, imagery, poetry, and language, some commentators have concluded that the novel's authorship is more likely Percy's rather than Mary's, though this interpretation is far from universal.
These arguments have been disputed as being mere coincidences. Leslie S. Klinger, in "The New Annotated Frankenstein" (2017), argued it is spurious to maintain "that the biographical coincidences of Victor Frankenstein and Percy Shelley are evidence of Percy's authorship". Instead, critics rely on the handwriting evidence and Mary's statements in the 1831 Introduction to the novel.
Proponents of Percy Shelley's authorship such as Scott de Hart and Joseph P. Farrell claim that he was obsessed with electricity, galvanism, and the reanimation of corpses, and point to the influence of James Lind, Percy Shelley's former teacher at Eton College. Advocates of Percy Shelley's authorship also point out that the novel contains his poetry such as "Mutability" as well as poetry by others, that the novel was imbued with the themes of atheism, social tolerance, social justice, reform, and antipathy to monarchism that only he advocated, and that there were noticeable motifs and subjects in the novel which only he espoused, such as vegetarianism, pantheism, alchemy, incest, male friendship, and scientific discovery.
However, editor Marilyn Butler, in her introduction and explanatory notes to the Oxford Press "1818 Text" edition of the novel, attributes these apparent coincidences to Percy's admiration and emulation of Mary's father, novelist William Godwin, whose works share numerous similarities in style, ideology, and subject matter with the novels of both Percy and Mary.
English literature scholars Phyllis Zimmerman, Phillip Wade, Stephen C. Behrendt, and Johnathan Glance compared the two early Shelley Gothic horror novels "Zastrozzi" (1810) and "St. Irvyne" (1811) with "Frankenstein" and found them to be precursors of the latter novel, containing the same or similar ideas, themes, structure, plot, and characters. Zastrozzi is a novel of pursuit and revenge where an atheist antagonist seeks to destroy his victim and his progeny. He can kill his victim at any time, but instead seeks to torture and slowly kill his victim by destroying and killing everything he loves. In "St. Irvyne", the plot centers around an alchemist, Ginotti, who has a lifelong goal to find the secret of life by the study of "natural philosophy", to attain immortality. It is also a plot of pursuit where the alchemist seeks to impart the secret of eternal life to Wolfstein, the protagonist. There is even a poem in "St. Irvyne" on the reanimation of a corpse, the nun Rosa. Both novels rely extensively on John Milton's "Paradise Lost", containing epigraphs like in "Frankenstein", and contain poetry intertwined throughout the novel, a distinctive feature of "Frankenstein" as well. These novels were also published anonymously.
Other authors have noted that Percy Shelley did not originate the aforementioned ideas, themes, structure, plots or character types. As Marilyn Butler observes in her introduction and notes to the "1818 Text" edition, Percy admired and sought approbation from Mary's famous father, in whose works can be seen numerous similarities with both "Frankenstein" and Percy's above-listed novels. Among these similarities are: tragic action narrated in the first person by an isolated intellectual ("Fleetwood" and "Caleb Williams"); enmity between two powerful characters with antithetical ideologies who pursue each other in a complex and shifting chase ("Mandeville" and Caleb Williams); and the story of a selfish intellectual who trades domestic happiness and marital love for scientific knowledge, success and power ("St. Leon"). It is arguable, therefore, that any similarities between Percy's novels and Frankenstein can be attributed to Percy's emulation of Godwin rather than his supposed authorship of his wife's novel.
In 1996, Charles E. Robinson published a transcribed edition of the "Frankenstein" manuscripts together with a chronology of the work's composition. From these it is possible to see that Percy Shelley's contribution to the novel is of between 5,000 and 6,000 words of the novel's 72,000 word total. Robinson wrote that from the manuscripts it was evident that Mary Shelley was the "creative genius" behind the work, while Percy's contribution was akin to that which a publisher's editor would provide.