They started as numbers, possibly assigned as rankings as of some date as
the more prominent pilots of the 1950s had the low numbers, or maybe they
were just first in line, I forget. Dick Schreder was "1", A.J. Smith "2"...
Then 2 alpha characters, George Moffat "XX"..., 2 alpha-numeric, John
Seaborn "A8"..., 3 characters came in about a dozen years ago as the 2
character supply ran out, Tom Knauff "JOY"...