I have never understood how Greg Jein's "T-Negative" fanzine article gained the support it did from people that fully knew what Jefferies' numbering system was supposed to represent. And importantly, in 1973 when the TM AND the T-Negative article appeared, as far as I know, of the two, only Franz Joseph had met and talked to Jefferies. It's no surprise then that the system he put together for his TM pretty closely follows Jefferies idea- that there were 17 starship designs that preceded Enterprise and that is what the "17" stood for. That's Jefferies, not Franz Joseph. But Franz Joseph met Jefferies when he was in Hollywood to go over designs he was developing for the new Roddenberry series Genesis II. He had just done the Booklet of General Plans and was working on the TM. It is hard to imagine him not asking the man that designed the Enterprise what he meant by those numbers. And as you might expect, FJ ends up telling us the first two numbers are related to the starship design. "5" and "6" for scouts and destroyers, "17" for heavy cruisers, "20" for dreadnoughts and "38" for transports.
I am sure Mike Okuda knew this since he certainly had contact with Jefferies, but he apparently still decided to go another way. I would love to know what happened. In later years Jefferies seemed disaffected by Josephs' work much as Roddenberry did, and loyalty might account for a lot. But for those of us trying to understand the state of things as they occurred, it's pretty clear. Franz Joseph was following Matt Jefferies' numbering idea, despite the differences in his blueprints.