The Entropy Effect
was the first original novel published by Pocket. In fact, its publication had to be delayed until Bantam had finished publishing the remaining novels under its contract, which was why there was a 2-year gap between Pocket's publication of the ST:TMP novelization and its publication of The Entropy Effect
I was going to link to Curt Danheuser's page about the Bantam novels, but I get a 404 Not Found. Is that site defunct?