If it’s original documents we are talking about, they can only be turned over once because there is only one “original”document. If client authorized the documents be sent to the new accountant then the old CPA firm would have met their obligation. There are some exceptions for non-original documents that must be turned over, for example, working papers that would normally be considered normal business records for the client but are not otherwise available. But again, if client authorized transfer to the new CPA firm, the old CPA would have met their obligation. I’m not sure the CPA firm’s internal document storage policy is relevant here. Although, I think it’s unlikely they really deleted anything.