How are paper authors uniquely identified? Some authors have an ORCID ID in order to be identified and distinguished in case of authors with similar name, change of name, different name format, etc. However, some sources don’t provide the ORCID ID of the author (if any exists), which causes a lot of problems when someone tries to harvest papers from websites with scholarly resources.

I thought that a combination of some author features such as name, email, and affiliation could be enough to distinguish the authors, but I don’t think this is a robust solution.

Is there any way to uniquely identify every author?
Aside from ORCID (which by far not every paper and person has), there really is no sure-fire way to uniquely identify an author. Using the name becomes problematic with common names (not unusual anywhere in the world, but a particularly common issue in Asia) or name changes (for instance in case of marriage). Combining with affiliation and e-mail address will also only get you so far as most academics tend to change universities at least once or twice in their career, and both affiliation and e-mail address tend to change in these cases.

For bibliographic research, the most promising approach is probably to combine all of the above with field information (e.g., a Markus Huber publishing in medicine is not particularly likely to be the same as a Markus Huber publishing in philosophy), and train some sort of heuristic classifier. Clearly, false positives/negatives will happen, but if your goal is to holistically assess a larger field of research a few false categorizations are unlikely to impact the overall picture too much.

If your goal is to assess an individual researcher, really the most accurate information is usually to trust what information the researchers themselves maintain (e.g., a CV or publicly available publication list).