Yes, sounds like you get it, Giant Wall changed so it gets rolled back to point A, then it resimulates, which might mean Giant Wall might push some other things this time around that it didn't before during the predicted simulation. It kind of uses a transaction log copy-on-write kind of mechanism, so there will be a log entry for previous value of the Giant Wall slot and it will restore that into its old slot. It's a bit more advanced than that but that's the gist.