My original GMRS call was KAE-6139. It expired and I was given KAE-9978 (my current call) when I reapplied.
I believe the original CB Class A calls may have been those weird ham radio-like calls like 19W2134. They didn't follow international protocol and the FCC changed them to KAA series in the very early 1960s.
The KA calls were reserved for Class A licensees.
Regular Class D CB calls started at KBA-0001 and were supposed to end at KZZ-9999. The CB craze of the 1970s exhausted those callsigns so another letter was added: KAAA-0001, and so on. All that went away with "license by rule", something I fear may eventually happen with GMRS.
Rick
Wellston Ohio USA
KAE-9978, KBA-3151, W8UU