Did Matt Jefferies own his creations, or were they the property of GR or the network? Maybe he would have had to buy a license or pay a royalty. Just because he created it doesn't mean the people he worked for weren't the legal "owners" of it. The expense of buying a license to use your own work very well could be enough to squelch any urges to do something like you suggest, no matter how well accepted.
Jeffries didn't own the rights to his STAR TREK designs; the legal ownership of STAR TREK was mostly split between Paramount and Gene Roddenberry.
Joseph beat Jeffries to the punch and scored financially when the getting was good (before anybody realized the value of enforcing certain rights).
But there's no indication that Jeffries would ever have created a blueprint package, even if there had been no Joseph. If Jeffries had published anything, I think it would have been a sketchbook of his rough set designs as viewed from an angle, like he always drew them, not a set of technical plans and orthographic elevations like (it turns out) the fans really wanted.
I read that the FJ blueprints would easily have been on the NY Times Bestseller list if they had been a book. But they were classified as a "special product."