I have about 250 songs in my iTunes Library with iCloud Status shown as "Matched" or "Purchased" but are not in my library. When I go to the iTunes Store to redownload, none of them are shown as "Purchased". I have been able to find some of these music files and relinked to the song file.
I would think that the ones I can't find would be available to download from "Purchases" or by finding the song in iTunes Store, and simply re-downloading. But the store listings don't reflect "Purchased" with a "Download" button. Rather, they have the price to be able to purchase.
I've double checked the song title, album and artist, and still not able to download without purchasing the music again.
I did see the suggestion to check "Get Info" and the account information on the Summary Tab, but it doesn't show any Account Info for many of these songs.