The A and B zones are going to be repeaters for the regional area; what's A5 for me locally will be different than A5 for your area. C will typically have some regional for the more secretive divisions and nationwide, and D is usually more nationwide.
Wayne, you are correct. Here is a channel list from an early 90’s FBI Saber from the midwest all with the famous PL of 167.9:
TX / RX / Alphanumeric
A1 163.8375 167.3625 Local
A2 163.8375 167.6875 Region
A3 163.8375 167.2875 North
A4 163.8375 167.2375 South
A5 163.8375 167.4125 East
A6 163.8375 167.5125 West
B1 165.900 165.900 car-car
B2 165.925 165.925 car-car
B3 165.975 165.975 car-car
B4 162.900 162.900 car-car
B5 162.950 162.950 car-car
B6 162.975 162.975 car-car
C1 163.9875 167.4875 Nation
C2 163.9375 162.6375 Nation
C3 163.8625 167.5375 Nation
C4 167.5625 167.5625 Nation
C5 173.3875 173.3875 Nation
C6 173.8125 173.8125 Nation
D1 168.8625 164.550 OCDETF1
D2 164.550 168.8625 OCDETF2
D3 164.550 164.550 OCDETF3
D4 168.8625 168.8625 OCDETF4
D5 155.475 155.475 Law MA