Check your system's Online Storage -- I can't remember if the regular matches are saved there, of just the favorites. And not completely sure how you'd get them back into the game.
But in general, the safest thing is to regularly make favorites of the matches you want to keep.
Just consider that with each patch to the game, the recordings before the patch will no longer work; so if you really want to hold onto something, you'll have to archive it to video.