It does not. I have made that mistake too and had to correct it. To use $mln to get the move number, you need to get $mline[$mln]->movenum.
This is somewhat important, because the first things that the HandleMove routine does in the betza.txt include after the move is parsed is:
set all == mln $maxmln; // indicates last move
Note there is no $ there, so we might be talking about different things, and this one might be a legacy variable. The purpose here is to determine whether the subsequent move generation needs to generate all pseudo-legal moves, and compare the input move against those for testing its legality. Or whether it can simply assume the move is legal, because it is not the final move of the stored game, and thus must already have passed the legality test on the turn where it was entered. If the latter is the case only the moves with implied side effects are generated, (e.g. e.p. capture or castling), for the purpose of reconstructing the side effect, and apply it to the board together with the entered move.
I cannot image how this would work if mln was not the current move number.
This is somewhat important, because the first things that the HandleMove routine does in the betza.txt include after the move is parsed is:
Note there is no $ there, so we might be talking about different things, and this one might be a legacy variable. The purpose here is to determine whether the subsequent move generation needs to generate all pseudo-legal moves, and compare the input move against those for testing its legality. Or whether it can simply assume the move is legal, because it is not the final move of the stored game, and thus must already have passed the legality test on the turn where it was entered. If the latter is the case only the moves with implied side effects are generated, (e.g. e.p. capture or castling), for the purpose of reconstructing the side effect, and apply it to the board together with the entered move.
I cannot image how this would work if mln was not the current move number.