As I say-- the actual bans seem to be carried out quite well-- and the inappropriate blocks seem to be quickly overturned. We seem to be quite good identifying actual sockpuppets of banned users.
There problem we do have is much much smaller, and relates more to incivility and NPA than to the banning policy. It involves not seriously believing people to BE a banned user, but sort of loosely tossing around the accusations of a vague sort of link to banned users. "Supporting" the banned user. "Agreeing with" the banned user. "Friends with" the banned user. "Your buddy" the banned user. etc. Alec ****** Such statements often have a bit more behind them than the people who make them are at liberty to disclose openly. Alkivar agreed with a banned user, for instance. He didn't get desysopped for merely having an opinion.
A certain relatively small core of banned users do collaborate together and they attempt to game the concept you articulate.
-Durova