My music files aren't missing, but iTunes has randomly lost many of them

Question

Most of my albums can still be seen in iTunes, but many isolated songs, and occasional whole albums can't be found by iTunes. I get the exclamation mark. When I look for the song files, they are right where they are supposed to be, in many cases right next to other songs which iTunes lists as accessible.
Looking for patterns, it looks like most of these "lost" songs are purchased. I can't see any pattern to why some songs on an album are missing, and others aren't, or why certain albums appear lost.
1. Anyone else seen this oddness? Why did iTunes lose track of the (normal) location of these files?
2. Is there an easy way to have iTunes rescan these locations without creating thousands of duplicates, or do I have to do this one song file at a time. (Ugh)
3. I do have backups, with Time Machine. I tried bringing forward and older version of the iTunes Library file, thinking that stored these locations, but that didn't work.
4. I can easily do a column sort in the detail view on any column, but I can't do that on the exclamation point column, to manually identify missing songs by grouping them together. I can't search for these other than by scrolling.
Any help would be appreciated

Answer 1

It seems as though Itunes is doing something very similar to the reason why I left Windows Media Player, it seems to be allowing the info such as artist, album, etc to be erased for some reason and then dumps the music into the unknown artist folder while leaving a broken link to the original artist and album folders.
this is a complete pain in the butt because I have over 22000 songs, and about .05% are displaced so we're talking about 110 songs that i have to go in individually and double click the song then choose to find the find and go through this entire list to find the exact song. What if 2% of my collections goes the same way I'm screwed.