Nyla and Angelas callsign

So in the episodes were Angela and Nyla in their detective car (6x7 and different episodes) their callsign is 2331. This makes no sense as detectives in the LAPD ride as 7-W. I don’t know if they just forgot about this or if there is a reason. Also its not just the number on shop cam, Nolan says it when asking Lopez to “10-3 to a backup channel”. I know this is minor and means nothing but I just thought of sharing it!