I'd be guessing how they wired them but I did two 3 story 30 unit modular apartment buildings so have an idea.
There was a lot of ENT installed in the building. Architecturally each building the same but not electrically. The modular sections were connected together with Molex romex connectors . So wire your units then at each section splice cut your romex and install male and female Molex , plugged together and mounted to small section of plywood for security during assembly.
For fire alarm notification circuits there was 3/4 ENT between the modular sections I'd couple together as the building was assembled or they were routed to the corridor.
Each electrical panel had large ENT going to the corridor.