I spoke to the very patient and understanding people of the Queens building dept.

Some of whom were irritated that I would not give a specific address.
What I got from them is the following (short version):
If the C/O states "cellar", then the below grade level should be found as unfinished, concrete walls and floor. This area is to be used for storage PERIOD. Even the use as a family room would be considered illegal
ANY finish "could be illegal". The only way to determine "legality" would be to compare the current floor plan with what is on file at the building department with an inspector.
The consensus was that ALL kitchens in the cellar are illegal and need to be removed.
THE HOMEOWNER CANNOT JUST REMOVE THE KITCHEN!!!!!
To legally
remove a kitchen (or anything else) require an architect to draw plans, file permits and have the result inspected by an inspector.
As I understand, if the C/O states "cellar" just the removal of the kitchen may not be enough to make the property "legal". It may also require the removal of all interior finish. The only person qualified to determine this is the building inspector.
I am working on a CYA statement. I'll post it later, maybe with everyone's help we can come up with a good one.