Ridba”z asks a question from a famous Yerushalmi that everyone knows from Torah and science debates. Halacha says that a girl’s besulim will grow back as long as she is under three years old. After that, if something happens, she has the status of a beulah. Let’s say a girl’s birthday is 15 Adar, and something happened to her on 20 Adar. She would no longer have the status of a besulah. But if Beis Din on 25 Adar declares the year a leap year, the Yerushalmi says a chiddush that her besulim grow back. Beis Din has the power to determine not just legal reality, but the physical reality of whether her besulim are there or not changes as well.
I’m not interested in Torah and science debates now, only in how this fits with our Yerushalmi in Megillah. If a girl is retroactively considered less than three and therefore still a besulah irrespective of which Adar is the real Adar or not, then why don’t we consider our korban retroactively to be less than a year old irrespective of which Adar is the real Adar or not? What’s the difference between these two cases?
I don’t think I understand the Ridba”z clearly, but from what I gather his answer is that there is a special din by korbanos that once something is nidche, you can’t undo the psul. If Adar 1 is the “real” Adar, and on the 15th of the month the korban was correctly declared pasul, then you can’t say that it is nidche v’chozeir on the 20th even if you add a month. However, if Adar 2 is the real Adar, then it turns out on the 15th you only mistakenly thought a year had passed. Really, it was not the 15thof Adar yet, but rather only the 15th of a tosefes month. That’s called nidche b’ta’us and the korban would be acceptable.
I'm wondering if you can say a different answer, and I admit it’s a bit shaky, but I’ll throw it out there anyway. The determination of besulah vs. beulah is a function of a girl’s development over a span of time. The question is whether the *span* of three years has passed. When it comes to a korban, perhaps the crucial question is whether the animal has had a birthday or not, i.e. whether a particular *point* in time has been reached. Where the concern is a specific point in time, then the question of which Adar is the real one is very relevant to whether that point has passed or not. If we are just measuring a span of time, i.e. have three years passed, then it makes no difference which month is the extra one. Why the focus when it comes to korbanos is a point in time rather than the span of time that has elapsed, I don't know – I’m just suggesting a logical structure in lomdus, not the philosophy behind it (Briskers don’t do philosophy, right?)