...Or at least such a system could be implied/established here, in a very convincing circular argument, by having Khan operate a ship that looks new and has the number to support it.
(Interestingly, TOS "Court Martial" already featured registries this high. So Khan's ship need not be brand spanking new, even if newer.)
Googling for 1864 gave me welcome education on the Circassian Wars but didn't turn up anything obvious regarding the Civil War. Where does the name Reliant
come from? It's an odd name as such, a starship that is reliant on others rather than stalwart or inflexible or vengeful or whatever...