The question isn’t strictly bound to rules – although sometimes there are mistakes about those too, the GM is kind of a novice – but is mostly related to reading some statblocks in the book. To better explain, we are playing a specific AP in which the party encounters a vampire wizard. In the book, a fight is contemplated and so there are stats for such enemy. It should have been a nightmare (a CR 14 against a lvl 6 party), but a very good build on my part plus some unlucky rolls on the vampire side (bless burst of radiance btw) allowed the party to win, although with serious wounds. But from previous experiences, I remembered:
1 – APs usually don’t put enemies of that caliber at that level
2 – if APs do contain such enemies, they put them in some obscure location after some obscure conditions (think of a "secret boss" or a "you effed up boss")
So in my curiosity I looked at the stats of the enemy (I know, it’s meta, but I didn’t read anything other than dead enemies’ statblocks, so it shouldn’t be that bad) and found out the GM used the stats for the same enemy but in a different AP (seems the vampire would have returned with more levels and abilities).
So that’s that, the party won thanks to an EXTREME dose of luck, because we were supposed to encounter a CR 10 (maybe 11, if an adjustment for extra players was needed) instead of a CR 14, but I understand this stat-swapping accident may happen again and we may not be that lucky next time. Now if my character dies it’s no problem, but I don’t know how the rest of the party might react in that case. Should I warn the GM or not?