The key point isn't if a claim is accepted or denied (the people getting the letters almost certainly have standing to be accepted), it's if there is money to pay the claims, and how soon they can get it. Having an unsecured claim isn't "Show up on Monday and the FDIC will hand you a bag of cash", it's "The bankruptcy court and trustees expect the final settlement to be in 3-5 years, with a haircut of 10-30%".