On Thursday I traced a theory back from 1935 to 1909. Asking colleagues did not help. Being in Europe, I didn’t have my usual handbooks available, but a search on some of the standard journal databases had turned up some articles after I experimented with keywords. One of these articles was published in 1935 and cited an earlier one in an abbreviated way. The abbreviations were still intelligible, so on Thursday I set about tracing down the works cited, but it soon became clear that something was wrong. The year number, volume number, and journal name were inconsistent: that volume of that journal was published in a different year. There was nothing by the listed author in either volume. One of the librarians at Innsbruck helped me figure out that the note had confused two journals by the same publisher, and that it was the journal name not the year or volume number which was wrong. This gave me a useful page of text and another two abbreviated citations. Some searches in library catalogues and Googling gave me the full name of one work cited; there is no copy in Innsbruck, on www.archive.org/, or in the Hathi Trust, and the Google Books copy is only available in three-line snippets. That is as far as I could go on Thursday; if I decide to pursue this further, I will need to order a copy of the article through interlibrary loan. Perhaps if I find it, I can understand the other note.
I wonder how many people have looked at these footnotes over the years, scratched their heads, and given up? One reason why many books today have an “abbreviations” section is that what is clear to members of one discipline today may not be clear to members of another 50 years later.
Edit 2022-05-11: fixed link broken when WordPress introduced the block editor