Just wanted to provide an update. I retained a tenant only attorney.
The first step is a letter to the landlord asserting the belief of the unit to be stabilized based on the available information and seeing what he comes back with to refute it (as he hasn't provided anything to show it should not be stabilized.)
We are FOIL requesting rent control cards (if any) and cases etc for the building. This will likely take a few weeks.
Long story short, and if I understood the attorney correctly, looks like it should be stabilized unless a rent regulated tenant was in the unit and market rent went above rent threshold.