My take: Upstate New York refers to the part of New York State (outside Long Island) that does not maintain close ties (in terms of commutes, etc.) with NYC. That means that, in general, any area served by commuter rail to NYC is out. Rockland County is not upstate. (Port Jervis may be an exception; I'd consider it borderline upstate.) I'd say that most of Orange isn't upstate either. Newburgh is borderline. Ulster is definitively upstate.
The NY 17 corridor presents a difficulty. Many New Yorkers spend weekends in Sullivan County (moreso in the past than today), but otherwise the area isn't really connected to NYC. I guess I'd call it upstate-with-a-footnote. The part of Sullivan closer to the Delaware is clearly upstate. And Delaware County seems more upstateish than most counties to its north and west.