I want to describe a project for categorizing 'old' things, as well as antedating things that may not be very old*. I'm looking for a word to describe their age.
First, I would like a positive or at least neutral connotation. "Antedate" is good in this sense, "old" not so much. (But I don't want to restrict the scope to just things that are known at the present but for which older uses are found, but also to include categorizing existing old things and discovering previously-unknown old things.)
Second, the term should not imply great antiquity. The things under consideration are a type of mathematical object and most will be fairly recent (19th or 20th century), though a few will be older.
Finally the term should not be overly obscure. Perhaps there is a common word which I have overlooked; if not, at least it should be a word with some currency.
At the moment I'm leaning toward "historical" which is not great but may suffice. Can you find a better word?
* That is, for something known to date back to N, find a use of it from year M where M < N. "Fibonacci's identity was actually first studied by Diophantus 900 years earlier."