65 Formula S info wanted

I recently bought my first A body, a 1965 Barracuda Formula S. I have extensive information and knowledge concerning 66-67 Chargers, but lack the same in A body cars.
My question is: When did Plymouth introduce the Formula S package to the public for the 65 Barracuda? My car has a build date of 12/11/64 and I have never seen an earlier build date on the Formula S car. Some information I have says it wasn't offer until the fall of 64...ie around October.
If someone knows, I would surely appreciate the information.
Thanks, Pat