I think these were more a turn of the century style holster. The most prevalent, by far, in this early period was the military flap and the California Slim Jim style holsters. To say it never happened would be a stretch but the Mexican loops and the variants, Cheyenne or Texas Jock Strap, each came along at or after the advent of the '73 Colt SAA. From the Civil War through the end of the century there was a great influx of gun models and style along with a proliferation of holster makers so anything could possible go by the mid 1870s when Mexican loop holsters and cartridge belts became popular. Packing Iron is a great resource for those interested in the history of early cowboy era leather.