If I encountered that, I wouldn't include it. But, I usually analyze apartments on a price per unit (or bedroom in some cases), so while I would consider differences in the gross building area for the unit mix adjustment, whether the units have interior or exterior entrances is also considered in the GBA differences for making that adjustment. So that wouldn't result in as much of a potential swing in value as it would on say a three-sided warehouse.
In my area, no. The majority of the apartment buildings show GLA (Assessor data, permit data, etc.). So in order to maintain consistency, GLA is normally the factor, not GBA. Although on very rare occasions, I have seen it used.
I wouldn't include it. However, I've always analyzed apartments on a per unit basis and generally only consider net rentable area as far as many any adjustments for different average unit sizes, etc. The only thing I use GBA for is the cost approach.
GBA (Gross Building Area) would only be used in the cost approach, and this complex looks too old for it to be a reliable approach. Stairwells are excluded from NET RENTABLE AREA, which is the sum of apartment living area. As an extreme example, buildings can have huge landings that also serve as common-area patios... these are not NRA and in market rent estimates they would be compared as tenant amenities.