First, full disclosure: Bill and I know each other and are not friends :-). Hopefully it's just professional competition but I rather think it's personal on his part.
Anyway, Bill's backstory is losing his revolver from his issued F.B.I. holster onto a Chicago street in the early 1970s, and 'inventing' (he didn't) the Kydex holster to keep that from every happening again -- to anybody. What we didn't know, because the info is always missing from his interviews into the present day, is exactly what holster he was issued from which he dropped his revolver.
As more and more research for The Book intersects, it has become clear that in the early 1970s, as a young F.B.I. agent, he was issued a Hank Sloan holster for a 4" M&P. Every agent was. And not being a gunleather designer then (and still not), Bill didn't realise that he had encountered the large weakness of the popular Tom Threepersons style holster (which was designed for the SAA and its long tapered frame near the guard and then had two and even three thick welts) when used with DA revolvers: the bearing surface for retention of the frame was very, very short (about 5/8"). Too short to be used without a strap, and the Sloan did have an adjustable welt but normally no strap. And the welt was only a single thickness.
sloan witty (1).jpg This is turnerriver's image
Had Hank Sloan (actually J.M. Bucheimer made the holster under license) used something other than leather for his adjustable welt holster -- e.g., I've used 1/4" thick rubber shoe sole material to good effect; glues and sands like leather, is thick, is grippy, and doesn't wear like leather and release the grip on the short bearing surface of the frame -- then likely Bill's accident wouldn't have happened at all.
Also perhaps it wouldn't have happened if the welt had been tightened against the revolver properly. Anyway, what he came up with was a forward draw holster of Kydex that encompassed the trigger guard but exposed the trigger. And had a safety strap! Forward draws were the rage then and his use of Kydex to replace the need to insert a metal spring was clever (also not the first to do that; the prototype of the Snick was first). But it turns out, that the forward draw spring action was entirely unnecessary to restore retention: it's the encompassing of the guard that does that (adding gripping surface and not relying on that short area of frame ahead of the trigger guard).
rogers smith.jpg Early '70s Rogers ad
To wit: his holster then, compared with the Seventrees IWB of several years earlier. They are quite similar in 'plan view', in fact. So if he had created ANY holster that enclosed the trigger guard hoop then he would have had the same result: enough bearing surface to keep the pistol in place. And makers like DeSantis of NYC did just that, following along behind Paris Theodore. Or just put a strap on the Sloan (which does exist).
x 1969 singles (1).jpg Late '60s Seventrees catalog page
I continue to be intrigued by how Bill's particular obsession with creating a secure polymer holster may have actually stultified pistol makers' focus on creating safer pistols: holster makers took on the responsibility and we got the Glock, a pistol that doesn't even have the safety features of an early 20th century Colt or Browning or Beretta.