I have a leather .45 holster with the stamp GYT-J.R.J. where the date stamp usually is. Not sure of that first letter, though. I assume it's a makers mark. Can anyone tell me what it means?

Here's a better example of that mark. BOYT - JRJ in a listing for a WW1 holster

 

Your M1916 holster was made by Boyt Saddlery during WW1.  The J.R.J. marking is for the initials of the government inspector.

 

Regards,

Charlie

Thanks, Charlie. There are slight variations to the US stamp on the holsters I'm seeing. Any relevance to this at all? Just normal variations by different manufacturers?

Yes, just minor variations between the different makers.  In WW1 the makers adhered very closely to the government specification for the M1916 holster so while there are slight differences in the markings and placement of them, the holsters themselves were pretty uniform.

 

Regards,

Charlie

I unraveled one and it's about 76 inches long.