Dear Haleivi and Sam,
Thank you, I am honored
Dear benignuman,
As I said, I have no definitive proof, but I will address your points.
1. Rabeinu Yerucham’s sefer apparently is well known for its’ typos. It is for that reason that it was hardly studied until recently.
2. It is a mistake to assume that just because there exists a position by a Rishon, that everyone knew about it. Rabeinu Yerucham was from Provence and after the Jews were banished from France in 1306, went to Spain and lived out his life there, writing toldos adam v’chava towards the end of his life and dying in 1350. As I noted, zero Influence on German custom. I would be shocked if his sefer was available in Germany at any point in time.
I will add to this point that because of the incessant geographical wars that were part of life in the middle and modern ages, there was often little if any communication betwen relatively large geographical areas; actually, insulation was the rule. This of course resulted in strong and unwavering, but very different minhagim developing in different areas. This point emphasizes the unlikelihood that Rabeinu Yerucham’ s influence was felt anywhere outside of Spain and Spanish custom, even after the expulsion in 1492 .
3. Even a Rishon needs a source. As Sam has vehemently argued ( I disagree with him, but his arguments are coherent and strong), innovative halachic positions still require a textual springboard. What was Rabeinu Yerucham’s textual basis for three hours? And why was he alone? After all, he did not live in isolation. Best answer: none, it was a ta’ut sofer and he never wrote it.
4. I would greatly hesitate before suggesting that three hours is a nice compromise between one (or none) and six, as neat as it sounds. Some may have escaped me, but I cannot recall a quantitative halachic decision that was settled by splitting that quantity in two. We may argue ad infinitum how large a zayit is , but no one says “let’s take the minimum opinion and the maximum opinion , average them, and presto! There is our exact halachic quantity”. One can hardly imagine a scenario where one opinion is that something is batel b’rov, another is that it’s batel b’shishim, and someone coming along and saying, “let’s stop fighting, just call it batel b’shloshim and we can all go home”