[Someone]

> A maximum of 8 pawns (4 white and 4 black, for example) can possibly be advanced over the course of the game to the opposite side

I think they all can.

If white’s A pawn takes a black piece in the B file and black’s B pawn takes a white piece in the A file, both white’s two B pawns and black’s two A pawns have a clear route to promotion.

You can do the same for files C and D, E and F, and G and H, at the cost of 8 taken pieces.

Of course, that “white’s A pawn takes a black piece” is wasteful in the sense that it is both a pawn move and a piece being taken, but I think it still is better than letting the pawns end up facing each other without being able to move more.