One thing I thought of a few years back. Ruth Berman's notes on Greg Jein's "Jonathan Doe Starship" talks about several different roles, with ships that are based on the same hull but have different internals to do different things. There are explorers, deep space explorers...I think scouts were mentioned. I always thought this would explain the wide range of numbers for ships which look the same, as well as the Archenar class. It wouldn't explain Jeffries' numbering plan, unless his "desgn" is the same thing as Berman's "role".