I think guessing the total amount makes for a good tie-breaker.

In terms of the contest, though, as long as everyone puts in an equal amount of guesses, it should all work out (i.e. 12 MM, 5 AE, 5 GA) regardless of how many are actually published. It also makes the last couple of months more unpredictable since there will be a variable pool of choices left given that Marvel won't actually publish 22 volumes next year.