Mistake in score card

I've never played in tournament or used a score card but I have watched videos and at the end of the match the players signed each other's score cards. What happens if the two cards don't match?

They must fight in a cage.

Maybe my club is sleazy and not doing things strictly legal, but I've never signed a scorecard (either mine or my opponent's), and I've never been asked to sign a scorecard. The only thing our TD cares about is that we both agree to the score we post on the pairing sheet on the wall.

Local tournaments post the pgns online, so they would need a score card to do this, right?

The local tournaments I've played in don't bother to publish pgns, so nobody even tries to collect scorecards. I guess that would be a lot of extra work.