You may well be correct. I do know that my roomies had the 5 speed. At the time, all of the "serious" European sports cars had 5 speeds in them. Of course, Jaguar was still running a 4 speed transmission.
But, hey, we were, for the most part, running a "3 on the tree" transmission. Mostly only trucks had a 4 speed and those had the "granny" first gear in them.
And, before someone cries foul... Yes, the Corvette had a 4 speed and it was an Optional transmission for other cars.
It took until forever for America to wake up to the efficiency of having a transmission with more than 3 gears. But then gasoline, at that time, was, on average, only around $0.36 a gallon. Who cared how lousy the mileage was?