I've noticed a few "late hits" recently. These are answers coming in months after the accepted answer. In one case of the answer came in 17 months late!
In that case, since the answer was a reference to a blog post written by the answerer, I questioned him in comments as to whether that was appropriate. I felt it was a bit spammy.
In a second case the answer is another tool recommendation. I wouldn't call it spam, since I don't know if the answerer has any association with the tool.
Are these cases something we should be concerned with? There aren't too many of them, so maybe we can just leave them alone.