Your repo remembers, even when you don't. This downloads your entire repo as one CAR and walks every collection in it — likes, replies, quote posts, reposts, follows, mentions, and whatever else turns up, including records from apps this site has never heard of — then keeps only the earliest interaction with each account: the moment first contact was actually made.
Public reads only — no login, nothing written anywhere. One request pulls your whole repo, no per-collection page limit. Give it a minute on a big account.