To date myself, I remember a time when 9-1-1 was NOT universal and payphones could be found every couple of blocks. In fact, one could receive calls at a pay phone! Every agency I have worked for, except ONE, was using paper logs and converted to a computerized dispatch system (four agency conversations).
All law enforcement departments use codes of some sort. It may be for patrol duties, warrants, or special circumstances but there are some. Others may have codes for unique situations. EMS and fire went to plain talk long ago. They discovered codes can be mistaken. There are no issues with the spoken words (well, not as many).
Belonging to an online Dispatcher group, one person asked about one particular code:10-7. This has a dual meaning for the agency in question. Out of service OR dead body. Hold the phone! If it's used, which one? That is confusing and hence the problem with dual meanings. Pick one and make a code for the other. This is also an excellent argument for plain talk and cell phones (call in the dead body) and say busy or not available over the radio.
Let's be real: codes were developed for two reasons in the 1920's. The first was to reduce precious time on the new resource. The second was to confuse anyone listening in, especially once the public found a way to listen in. The second reason became useless once Radio Shack started publishing their radio frequency guide with various codes listed. The internet made it stupid with lists of local codes.
Give up the codes!