No simple explanation. They are British cartridges. I dug the following out of White & Munhall, Volume II: .455 Eley is a name applied to .455 Revolver Mks I & II. The .455 Revolver cartridge was first made in 1892. There was no ".476 Eley" cartridge.
In the 1870s, the Brits used a "450 Revolver" cartridge for the Adams. Both the revolver & cartridge were less than successful, so in 1882, the Brits replaced them with the Enfield revolver. W&M said the Brits never applied an official caliber designation to this revolver. Inside lubricated cartridges were labeled by the cartridge manufacturer as ".455 Enfield". Cartridges loaded with heel-type bullets were labeled ".476 Enfield". Both were intended for the large Enfield revolver. The Enfield revolver was replaced by the Webley in 1892. Apparently, all of the multitude of .450 & .455 & .476 Revolver cartridges are interchangeable. This was too confusing, even for the Brits, so in 1892, they replaced (or re-labeled) everything as .455 Revolver Mk.I. With a shorter case and smokeless powder, the cartridge became the .455 Revolver Mk.II in 1897.
Whenever anyone attempts anything approaching the encyclopedic and technical, errors will occur. Frank Barnes started out to provide some information on 1500 of the world's more common cartridges. While Barnes kept control, some of the errors were corrected. He never got around to correcting the information on British military revolver cartridges. After Barnes' death, the publisher has used COTW as a cash cow, putting very little effort into correcting known errors, making more errors, and generally letting the quality of the work slide from pretty good to downright sloppy & shoddy.
Richard
