Interesting! Well, I called the humane society and asked whether they had any records showing that he had indeed been neutered, and they got back to me later and said they showed that he'd been neutered on 8/25/99 (he was over two--isn't that kind of late?), and that they had double-checked with the hospital that performed the surgery. I called my vet as well, and they said just to keep and eye out, and that if I saw it happening more frequently, or if he began to lick/bite the area, to bring him in.

It will be hard to watch for this, I think, because as micki76 indicated they disappear as quickly as they appear! But I am glad to know for sure that he's neutered.