If you have one that is overstruck, it would be that the -2 was struck over the -0, not the other way around.

A few here have reported and posted guns that were actually struck as -0 but they are few and far between in the scheme of things. I don't know if anyone really knows why they were struck like that (with the -0).

I agree with Jim above. Get yourself a copy of the SCSW 3rd and read it. It will answer many questions for you.

As for frames, serial numbers etc., since all N frames are the same, they were forged and serialized, then pulled from parts bins and used as needed, so one could have been used for a 29-2, and the very next numbered frame could have been used for a 25-2 etc.