Moderation/blacklist filter

I use IP addresses to moderate or ban various commenters. When I want to unmoderate a commenter I find the IP address and remove it fr. the moderation list. But I’m having a problem with a commenter who I want to unmoderate but I can’t find anything related to him (email address, IP, nickname) that is in my moderation list.

So I’m wondering if it’s possible that because his IP address contains the numbers “188” that other IP address containing the same number sequence & which are on the moderation list may be flagging his comments for moderation?

Is that possible? It seems unlikely, but I can’t figure out what else it could be.