They don't send out notices they just cut your IP.
So some have several IP's, Friends or a smarter computer tech.
Many would be surprised just how intelligent the forum software is. Most times the forum administrator knows instantly If someone who was banned previously comes back under a new name however we generally just let them go until they become a problem.
Only the forum administrator, Okuma Steve, has access to user accounts and the ban lists. The rest of us are simply moderators.
I hope that clears things up, Wayne.