Comparing games with that notation alone would make moving your queen e2-e3 in game A the same as moving a pawn e2-e3 in game 2. I don’t think anyone would act

Comparing games with that notation alone would make moving your queen e2-e3 in game A the same as moving a pawn e2-e3 in game 2. I don’t think anyone would actually agree those are the same move. What Stockfish considers a move includes the full board state, it simply doesn’t need to pass that information around internally. Thus removing that ambiguity but means there’s a great number of moves that have only occurred once. Also, it’s 6bit + 6bit + 2bit + 2bit = 16 bits which isn’t an arbitrary number. There’s no need to actually encode that something is a promotion because it can be inferred from the board state, but there’s zero cost to pass an extra bit around so it’s included anyway.