So I just clicked "approve" on a reader's comment -- and then couldn't find it on the post. Turns out Blogger had shuffled it into spam.
I went into my blog's spam file and found the reader's comment -- as well as a whole bunch of other comments I had never seen and certainly had no intent of filing as spam.
To anyone who kindly posted a comment at some time in the past and then were puzzled when they never appeared, I beg your pardon. I had no idea Blogger would automatically shuffle comments into spam; I thought all comments, even those which clearly are spam, came through for my approval.
Guess I'll start checking my spam folder more often.