Parker Pages arrived here on the Washington/Idaho border Friday. Good to have an explanation of the 12A and 12B brass cases. I have found the A and B caveat for brass shells in the 1877 E. Remington & Sons catalog and the 1880, 1882, 1884 and 1885-6 Union Metallic Cartridge Co. catalogs. Here in the 1885-6 --
1885-6 Catalog page 12.jpeg
By the 1887 Union Metallic Cartridge Co. catalog the A and B caveat is gone.
1887 Catalog page 18.jpg