>it's at this point you tell me the OED cites thwack from about 932AD..

wrong, duack-breath. but it did come along about 1530 ce, as we find Heywood writing, "I shall bete her and thwak her." and the venerable bard, in 1607: Here's he that was wont to thwacke our Generall, Biggus Martius., proving once again that he fronted the blacklisted Julius (Kaiser) Brooks.