In the last year or so I've had periodic trouble, some of it my own fault, messing up my iTunes library, then I switched to a new computer and am not using my old one anymore.
As a result, some of the stuff I bought at iTunes didn't get transferred over, didn't make the jump somehow. And some of it I fully expected to be there when I opened iTunes. I definitely don't remember deleting it. But all these troubles have happened.
One thing I bought at iTunes (and I don't buy much there, since I like Amazon a lot better) was Stephen Colbert's Christmas album, which is basically rotten but I wanted to hear a couple things off it. Well, it wasn't there ... and except for a single backup I had of it on a hard drive, unknown to me except it was found by searching ... I wouldn't have it now. That was OK, I reloaded it and it worked fine.
But I had another song from a little longer back, when they had protection on all their tracks. And it was the same situation, suddenly missing. Still, I found the backup and transferred it over, and guess what, it wouldn't play ... not until I typed in my password to prove I'd bought it once upon a time, at which time I was informed that I could put it on 3 more computers! Meaning I only have 3 more shots at losing it and needing to get it back. This a track that I bought.
Too bad about that DRM crap. What a bad idea that was. You'd think somehow, now that they don't do that anymore, that they could make it retroactive on these older tracks.
I don't like any of those shenanigans. Which is why I started getting tracks at Amazon in the first place.