I finally found the place where Blogger stores embargoed comments which it thinks are spam. I just released about thirty or so of readers’ blocked comments (most of them by Zenster). I tried to delete the duplicates where I could.
My guess is that the spam-detecting algorithm, among other things, counts embedded links and marks a comment as spam when it contains more than a certain number of them. Zenster and heroyalwhyness like to include links, so this may be why they were targeted repeatedly.
The good news is that the filtering software really does seem to catch the referrer spam. The bad news is that I will have to remember to visit the embargoed comments every day or two and release the mistakenly blocked comments.
I recommend that commenters try embedding no more than one link in any given comment, and see if that helps.
[Nothing more here]