grenv:
"point 1... Move 40 is defined as being different in the rules... assuming that it should behave the same is plainly wrong."

Plainly (please read for yourself), there is no such definition of moves 20, 40, etc., being inherently "different".  But by rule something special does happen after each of those moves (assuming, of course, that the game does not actually end on any of those moves.)  I do hope you agree that a game can be ended by a black move 20, 40, etc.

"point 2... Actually my sequence is the same as yours, I just have a different definition of checkmate... my definition is;
"if the white king is in check and cannot legally move out of check on his next move, then he is checkmated." "

Checkmate ends a game.  There is no "next move".  Plainly, the mating move is the last move of a game.  So any definition that demands a reference to a "next move" must be doing so in a hypothetical way, as it refers to something counterfactual--it will not occur.  In my opinion, it's better to avoid that in a definition if that can reasonably be done.

Your definition appears to be:
"if
the white king is in check and could not legally move out of check next
move in an identical situation in a different variant, then he is
checkmated"

Plainly not.  My test for mate after Black's move 40 would be the same as the test applied after moves 21 through 39.  I think that would be the same evaluation applied in conventional chess.

And please tell me when you perform the test for mate: before the ice age?