Honestly now I'm more interested in WHY that simple code is used. Could be that
1. If used with a code that requires a separate software to decrypt and decode it, BO would just rummage through the phone to hack into it and there'd be no need to interogate the agents one-by-one to find out HOW to find the home base but instead it's HOW to use the software.
B. There is no primary home base in this op. Locations shown seems to be only rendevous points. In theory, without a specific home base meetups points would change locations frequently and there'd be no need to call off the op but only send in more agents if needed, leaving BO scrambling to chase the next agents to come on the basis of not knowing that there is no home base to chase. Seems to be working, if it weren't for the cheap ass code.