Just a quick clarification. The FM Erie Built was Fairbanks Morse's first attempt at a road passenger diesel. They are called Erie Builts as GE assembled them in their Erie plant as FM did not have the ability to assemble them at their own facility in Beloit, Wisconsin. The PA was an Alco product and was in direct competition with Fairbanks Morse. The opposed piston engines were the downfall of the most FM locomotives, so they didn't have the longevity or the sales that the PA saw.
The Alco PA was their 2nd attempt at a road passenger diesel after the DL series whose development was cut short due to WWII. Alco had its own issues with its 244 prime movers which is why EMD which was already the established leader in diesel passenger road power prior to WWII ultimately became the dominant supplier of passenger locomotives in general.
The math speaks for itself. 82 Erie Builts A units were built versus 169 PA1s. Compare that to 429 E7s alone built roughly during the same time period as the Erie Builts and Alco PAs.
New York Central purchased 4 A units for passenger service and 8 for freight. The two B units were used in freight service. During this time, the New York Central standardized on two tone gray for passenger units and black and gray for freight units.
This is merely speculation, but due to the reliability issues I would think all the NYC units ended up in freight service fairly quickly so running the A and the B you have is a pretty likely scenario. However, I'll leave this part to the resident NYC experts of the forum.