But it's over with an illegal move (haven't used both dice numbers). We should investigate after every move if the move played was legal or not.

If we don't do that as you suggest, someone can for example in the start of the game having a 42 to play, to take all checkers claiming that he won........

So since the move 2-off is illegal the game can't be over with an illegal way.......

I'm always serious.......!