On the Blogger Dashboard, when you click Comments, it shows Spam, Published, and To Be Moderated. I have comments older than 2 weeks requiring moderation. This keeps spam comments from popping up unnoticed on old posts.
I've also requested an email when I get a comment that's waiting for approval. More often, they just go to the file "comments waiting for moderation" without sending me the email notification. I finally realized how often this happens when I checked the file the other day and saw nearly a dozen really great comments on older blog posts. There were even comments from last year!
I quickly hit "publish" , feeling bad that I'd missed them at the time. I've been on Blogger nearly ten years and still it seems there's always something new to learn!
Do you require older comments to be moderated? I highly recommend it, to avoid sick crap from showing up on past posts. I also recommend checking the file regularly so as to not miss them!