Who or what is your source for this info? Never heard of any state prohibiting interest accrual after closing an account. If that were the law, one could default on their mortgage, car loans and CCs and just keep paying off the balances interest free. You find that law, lemme know. I'm gonna be buying some real estate in that state.
Some states prohibit CAs from continuing to tack on interest after they purchase an account. However, if one is suing, even a JDB, they can probably get statutory interest on a judgment from accrual date--which is when they bought the debt.