Nathan Altice asked on Twitter why authors say that text will appear “below,” which led to a discussion between Nathan, Paul Benzon, and myself.
After I got home from watching a live satellite screening (the future is amazing!) of the Hot Docs presentation of Indie Game: The Movie (which I highly recommend for all those interested in videogames and the people behind them), I started looking a little more into the data that I’d found. As I suspected, the early blips in the ngram were largely due to errors in metadata, appearing mostly in footnotes added by modern editors in a later edition of the work. That said, some of these blips did contain applicable uses of the phrases in books like The Fredrician Code, published in 1761, where the phrase “see above” appears, referring to clauses of law that appear earlier in the book, much the way we would use the phrase today. That said, these blips are relatively rare, and it’s not until the 1800s that the phrases really start taking off and approaching levels of use that we see today.
I thought that it could be that pre-1800s there were more uses of the Latin equivalents “vide supra” and “vide infra,” but rather curiously the ngram of these phrases wasn’t that far off of the ngram for “see above, see below,” all things considered—they both start right around the 1800s and build from there (although the Latin phrases seem much more erratic in their uses, and fall off in recent decades). I also tried searching for the abbreviations “v.s., v.i.” and “v. s., v. i.,” and got precisely zero results each time (something that I suspect is an error, as I find it hard to believe that the abbreviations were never used in print). Even if I were to find instances of the abbreviations, however, it seems highly unlikely that they would differ too much from the full phrases, as writers would be unlikely to have spent the 1700s using the abbreviation only to switch to the full phrase in the 1800s.
Ultimately, this is just an initial search, and there’s a lot more we could look into, especially if you consider works in other languages, as well as in time periods not covered by Google Books. I would encourage you all to add comments to this post—this seems like the type of question that would benefit from the knowledge of many scholars of diverse interests..