Just a quick note. Ketubot pg 9.  Kohen A priest marries and finds his wife was not a virgin, she is forbidden to him because of a doubt,--the act of sex was before or after Airusin [engagement]. Tosphot: why not say hezka every person is in the hazaka of being OK until proven otherwise. Answer: because hazaka from the start. That pushes the time of sex as close to now as possible.  R. Akiva Eiger: Why not say like the mikve that was found lacking. I.e., Hazaka of OK with hazaka of now [present status] pushes the assumed time of sex to before the Airusin.[in which case she is permitted to her husband.] Rav Shach brings an idea from the Rashba that answers this. You only use hazaka of now [present status] in a case where you do not know if an act occurred--like the case of pure things which were dipped into the mikve. We do nor know if any "act'' occurred since the mikve is now lacking the 40 seah. But in the case of the wife of the priest we know she was not a virgin at the time of marriage. So there hazaka of now [present status] does not apply.

Why does this come up?, you might ask. The answer is there is an argument in Gitin between Ramban (Nahmanides), Rashbam, and Rambam about the need for the date in a get. And from what I can tell Tosphot is being consistent with his approach [Gitin page 86] that when we know an "act" occurred we use hezkat hashta [present status] to push the assumed time backwards.] but I am very full of hope that God may grant to me to  think about these issues at a future time. I just wanted to write down some of these basic issues. [So far I am thinking that Tosphot is being consistent. But then the questions would automatically arise about the Rambam, Rashbam, and Ramban how to answer the question that Tosphot brings in Ketubot page 9. [which I might mention is perhaps the most famous page in Shas or at least second place to Bava Metzia page 100.]