Regarding the building, my guess, without seeing the plan, and Markmax33, correct me if I am wrong, are in a Guard Armory or something similar.
The primary occupancy is Group B and the corridors probably serve the Assembly and Business use areas. The corridors are not counted in the Assembly use because they are not simultaneously occupied by the assembly occupants. Meaning, the folks in the assembly areas are not ALSO in the corridor.
By allowing the total occupant load of the assembly areas to be added to the load of the balance of the building, corridor width will be addressed properly.
Calculation of assembly is based on the NET square footage of the assembly use space which increases the load to be served by the corridor.
MM33 did not indicate any intent nor would it be required, to separate the two occupancy uses. If he uses the "non-separated" permissions of IBC 508.3 and protects the building according to the most restrictive applicable provisions of sections 403 and Chapter 9, then all is well on the home front.
Note that Section 508.3.3 states "No separation is required between non separated occupancies".
I rest on my case! (or something like that)
(being a damage controlman helps you understand how to fix stuff)