Well, I don't let my license expire, and I also carry another couple forms of photo ID. Still, though, if the State of Tennessee considers my expired license valid for identification purposes, so should LSAC, at least when I'm in Tennessee.
This could also be a case of a test center worker being a prick, as well. They don't make copies of the IDs or anything, so if I were the test center guy, I would have let him through, even if the policy is to not do so.