One thing to consider, once a game starts, then it's considered a win. I used this before. If there's a 3 team multi and one game gets cancelled for any reason, you get paid for a 2 team multi. This includes rain out, cancellation by the book, or any other thing that caused the last game to be cancelled. If 2 games are cancelled, then 1 game is good. You can't wipe out a multi after the start of the first game.
In this case, we are not discussing about individual selections but an entire betslip with more than one selections. If a slip cancelled for any reason then the stake should be returned, no matter later when all results are settled then one or more selections are wrong or all selections are correct. It sucks when all selections are correct but it's a nice incentive when you find at least one of your selection was wrong but you got your stake back because the entire slip was cancelled.