New Jersey (in my day) was full of split-bus panels, mostly FPE and Murray, 60 amp "lighting" main for the sub section.
The DC metro area also had them quite frequently, especially in total-electric homes since 200A main breaker panels were still fairly expensive back in the 80's.
I remember some of the larger ones even having two sub-sections, thus limiting the mains section to only four disconnects. We would often find all single-pole circuits in one sub-section and heating/AC loads in the other, leaving the dryer, range, water heater, etc. breakers as
mains.
No matter the location, hack jobs almost always resulted in single-pole breakers ending up in the mains section or <gasp> some Harry Homeowner managing to cram twin breakers in those spaces. Ah yes, those were the days.....
