There was a thread on UKGSER with a chap who had sent his licence back for renewal and the same thing happened, the difference was, he did have a copy of his original licence, but they apparently would still not reinstate his entitlement, so he had to take his test again. Apparently they wanted a copy of his pass certificate. I'd be stuffed if that happened to me, but it seems if its already on your photo license, then it will be there. You can log onto the DVLA and it will show you your licence entitlements, so if its showing there, you will never have an issue.