Other people more expert than I will likely chime in soon, but I can give you a start.

1) basically Same Day Change is a Y offering. You weren't denied your first class seat, as you could have had your first class seat on your original flight. Voluntary changes do not protect you in first in the same way that an Invol change would. I'm wrong here. Accurate information given below.

2) the fine print on the EQP promo excluded mistake fares, so I doubt it, and it might be wise not to draw attention to your account if you got 2x on all the other segments.

3) The sticker earning year begins 01 March each year, so check you're counting from the correct date. As a rule, though, I think stickers sometimes take a day or two to catch up with posted miles.