I bought an "old supers apt" Co-op

Wouldn't have been surprised if your place was in the UWS. Happens a lot and is discussed in depth in this Hauseit forum thread:

https://www.hauseit.com/forum/forum/selling-real-estate-in-ny/543-selling-a-below-ground-basement-apartment-in-nyc

I bet it was completely below grade previously. They needed the staircase to be able to sell.

I'm actually in Yonkers which isn't NYC anymore I know but just looking for any previous scenarios, I found something in the Yonkers code book under zoning that states, if more than half of the space is above ground is above ground it is a basement and not a cellar.
I wouldn't advertise it as an extra bedroom but more of a storage or gym space which I'm currently using it as.
Could I be opening a can of worms for myself by digging further with the city?
There was an issue with the electricity after I signed and the previous tenant took out the last of his stuff the power was "cut" and took me ages to figure out what the problem was, the super couldn't explain the new 2 breaker panel in the buildings electrical closet marked for my apartment... clearly for a washer dryer