When it can't find the file, there is a little (!) icon next to it. Though a details button would certainly be a step up.
Oh, I assumed it was just leaving it out of the list,which would have made it much tougher to find.
I dunno, some people on the Apple board are saying it could've been easier, just copying some directory wholesale, but I did some research and I think since I hadn't been letting iTunes rearrange my files (I do now, but the machine I was leaving didn't have enough room) this might've been closest to my best bet.