Must bibliography entries match the original title's German orthography? I am writing a book, and in its bibliography I would like to include a paper whose title has the German word "Über" printed as "Ueber". As far as I know, this is an equivalent way of writing the word, but the former way is the normal way. It is definitely spelled as "Ueber" in the (nineteenth-century) journal in which it appeared - the body text uses umlauts so I assume there was some typographic obstacle with the title font.

I can see three options for me:


Ueber
Ueber [sic]
Über


I have a soft preference for (3), because I think it looks nicer. I do not like (2) because it carries the implication that Ueber is an error, which it isn't. But (1) is the original form. I could just about imagine somebody failing to find the paper because I wrote (3) instead of (1), but it seems unlikely - search services like Google "know" about the equivalence, and readers will have the volume/page/date information regardless.

The publisher has asked me to follow Chicago Manual of Style guidelines if in doubt. Unfortunately, I cannot find a definitive ruling there.

Am I bound to use the precise conventions of the original publication, or should I adapt to a more normal modern style?
I would always prefer the original title of the paper (only ignoring all-caps or similar), even if it contains spelling mistakes, as this is the most likely search term, somebody is going to use (and not all search tools do autocorrections). This in particular applies to titles in spelling conventions that readers might not be familiar with. A German paper from that time might use the spelling Oscillator instead of the modern Oszillator or Maasssystem instead of Maßsystem¹ – would you also change these?

As a sidenote:
Uppercase umlauts (such as Ü) only came up in German in the nineteenth century and were only fully established as a consequence of the spelling reform/establishment of 1901. Thus, it’s very unlikely that Ueber was used due to typographical restrictions and one could argue that it is the more correct spelling here. Also note that nowadays, substituting Ü with Ue is only allowed as a makeshift solution and the two are not regarded as equivalent.



¹ Taken straight from Max Planck – Ueber irreversible Strahlungsvorgänge.