The best way to look at things is that in the HGVC deeded system, there are two types of points, "ClubPoints" and "by Hilton Club Points." I am specifically using the terms as they are used in the HGVC rules and on the web site; sometimes you see them referred to as Club Points or bHC points. Those are the two buckets that exist in the HGVC system.
In the HVC (former DRI) system, there are a number of different collections that form other buckets for the points native to that system. As a retail HVC (trust) owner, your points can be used in the entirety of the HVC (former DRI) system, which is confusingly called "The Club". The points you own there have the native reservation windows and limitations of "The Club". In my experience, the cost in MF/point for the most efficient collection in the HVC system that I know of is ~$0.1542/point - I own a resale contract for Cabo Azul and have been told that's the cheapest there is there. There might be others that are less expensive, but I don't know of them.
If you were to add a resale deeded ownership in NYC, that ownership would not be in the MAX system, which is the overarching inter-system exchange system HGV has set up between the deeded and trust programs (which will also incorporate Bluegreen sometime in the future). HGV will allow an owner in both the deeded and trust systems that is in MAX to call in to combine points for a reservation made through the MAX exchange - accomplishing that without calling in doesn't seem to be in the cards. IMHO, if you were to add a resale bHC ownership, you could use that by itself for a reservation in NYC but it's questionable whether it would be worth using the trust points there because they aren't a great price/point. My cost for bHC points is low because of the deeds I own (The Quin penthouse units), but at The District, which is fairly well available resale, the costs are around $0.16 per point IIRC. There are some bHC deeds with much higher costs, of course, but you should be able to avoid those with some research.
Bottom line is that you are best off using the trust points in the trust system; if you can get a good reservation at a good cost in the deeded side of things, go for it. You will have access to discounted bookings when they are offered, which is a good thing. I think the only way you would actually be able to combine the points for a single reservation would be to purchase retail from the developer either as an initial purchase or as an upgrade of a resale ownership. Either of those can be expensive.
