Did you buy some partial albums? If so, they don't show you the album, they list whichever tracks you bought (that they now offer in iTunes plus mode for 30c) separately in a split browser window below where they show your albums.
At least that was the case for me. I think if you upgrade those tracks, then go to the album in the regular store you will get a regular "complete my album" offer in iTunes plus. But usually if you only bought some tracks then you wouldn't want the whole album anyway...
In some cases, the partial-album track list upgrade offers seem incorrect, or incomplete. In a few cases I had bought say five tracks off an album, only four of them were offered as upgrades, and yet if I looked in the store itself, the whole album (say 11 tracks) was available in iTunes plus. So I wonder why I couldn't get my fifth track for 30c. It seemed only way I could get that missing track was pay 99c for it again.
And I'm a little suspicious because the track I was not offered to upgrade was a very popular one on the album, although it's not pegged at $1.29 in the store now for the iTunes plus version. Maybe the label had wanted to charge $1.29, and the compromise was not offering it as a 30c upgrade to people who already paid 99c for the old version.
Yah so then if I buy that track I will have shelled out 2 bucks for it in the old and new formats...