I had purchased over $1000 worth of music from the iTunes store and still have every email receipt to prove it, but a few years ago I lost my hard drive containing my iTunes library. I tried the "Check for Available Downloads" option in iTunes and nothing showed up. I contacted Apple and was told that none of it was available anymore. I checked and the music was still there. Apple then told me it must have changed format or something, but that I would have to purchase my music again. AND this was before the cloud. iTunes store has always been that way. Total BS
Why don't you look at the Purchased section of iTunes rather than the "Check for Available Downloads" which doesn't even do what you want it to do anyway.