The apartment building mentioned in the thread title (well, OK, it just said apartments and nothing about the building) seems to bring it under 240.24 all right.
But that just talks about overcurrent devices, plural and does not seem to cover whether this has to be a single main or just all of the individual breakers.
What does raise a question for me is the scope of "protecting the conductors supplying that occupancy". To me, unless tap rules are involved, nothing in the panel in the apartment protects the supply conductors
to the panel, just the feeder or branch wiring inside the apartment.
I thought I understood this section until today.
The exception in (B)(1) only addresses the OCPD for the service itself and feeders that supply more than one apartment.
If the question ultimately revolves around doing electrical work in the sub-panel (like changing out branch breakers with the main open versus with the bus energized, versus having the management disconnect the feed to the panel), that gets into a whole different area of concern, since 240 is just talking about OCPDs.