I don't know if this is the place to discuss this, but it is related to my problem and I have not found anything closer. I had too many songs for iTunes Match, so I created a new, empty library. When I signed up for the service, the only things that appeared in that new library were cloud versions of past iTunes Store purchases, which were available for download at my option. The problem is that certain songs and albums purchased at 128kbps that I know are still available in the iTunes Store were missing. In the case of individual songs, most of those songs are greyed out on the track listings of the albums from which they come, indicating I purchased that particular song from that particular album currently available in the iTunes Store. I don't know how to tell whether an album I have purchased is same version as that currently available, but most appear to be identical (I have noticed that "remastered" or "bonus tracks" versions or albums that have had other modifications may not match if the original purchase was not so enhanced but am not referring to these). The bottom line is that I cannot download 256 kbps versions of these songs.
I have refreshed and re-loaded iTunes Match several times with the same results.