I'm just realising that I did this study for Phil and am only now thinking of posting it on this thread: a comparison of the construction details between a known Rabensburg (has initials stamped into the cuff using very unique stamps) and a known Brill (pics by bmcgilvray here) stamped Brill on the cuff.
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There are NO differences; even the stitch count on the left side sewing, and then on the right side, of the cuffs is the same between the holsters. Note the odd stitching (special machine of some sort) at the muzzle, showing only on the backside view, is identical (but different from the welt stitch and the lining stitch and the two cuff stitchings); it looks quite like a chain stitch but I've never handled one (the Brill I bought on 'that' site was not delivered).
If I haven't suggested it before, I reckon that all the makers being in Texas, that perhaps they were effectively serving the different Texas Rangers Companies geographically divided around Texas; and could even have been founded by former employees of the better-known makers of the Brill style.
Based on the rear view of lawandorder's holster, I'd say "not a Sessums" based on the sewing there of the cuff. And all those little ridges on either side of the very fine sewing of the lining are from the lower feed dogs on the flatbed machine that was used (saddle stitching machines are needle-feed and have no feed dogs; so leave no marks in the leather).