The 1877 E. Remington & Sons catalog offers 2 5/8-inch No. 10 brass shells in A & B.
The 1880 UMC catalog offers No. 10 brass shells 2 5/8-inch and extra-long to 3-inch.
1880 empty brass shotshells.png
A & B shells are mentioned in the 1880, 1882, 1884 & 1885 UMC catalogs. No mention that I've seen of A & B shells in the 1887 and later catalogs.