Came across this thread and noticed that I had been referenced as stating that there was only one factory MG38B in the NFRTR. As a great fan of the MG38 and MG38B I'll post some of my experience with these MGs.
The gun to which I was referring was owned by Dolf and in the inventory of his MG parts business, ARPAC, Inc which he ran out of both San Antonio, TX and and also I conjunction with a friend in CA in 1970-1990s. I received his periodic mimeographed guns and parts lists, which showed up about once year. In the listing for Jan. 1982, there was the ad for an MG38 in 7.65 Arg. with an array of accessories including a complete spade grip setup to convert to the "B" configuration. I called Dolf and talked with him about the MG38 about which I knew very little and was interested in knowing more, which turned out to be a very unusual model but the price was way beyond my means. Anyway, Dolf said this gun was the only one he had ever come across that was original. No reason to doubt that since no other original, factory MG38s have ever been acknowledged or confirmed. I stilll have the ARPAC list from 1982 with the ad for the MG38.
DLO imported a quantity of Colt MG38s and 38Bs from England but I don't have the number of guns or dates of import in front of me. I visited DLO in Stamford, CT quite a few times from 1971 until the 1980s, having grown up in the next small town over, I did not visit him again after he moved to Torrington in central CT. I don't remember when he started building the 38s. I bought a total of four of the MG38s from him over a period of time in the late eighties and early nineties. I still have three.
Here's the interesting part. He marked the MG38 right sideplates he made and registered with the same format, style and ID info as the original Colt's were marked using Colt's Hartford address, etc. He did not do that with his other sideplate WC MGs, 1917s and 1917a1s but put his Stamford, CT license address on those guns. The markings are engraved and not roll stamped.
I had heard about the MG38 that Stewart handled and have no reason to doubt that it is the one that Dolf had all those years ago. FWIW