First off, I'd like to say that I personally want there to only be one killer for all of these possible victims because that means there's only one bad guy to catch & when he's caught this will be over.
However, I tend to think we're looking at two killers here whose dumping grounds (& hunting ground of the huge metro-NYC area) overlap. But I go back and forth.
I live in south Louisiana, and we had a serial killer who scared the carp out of the region around Baton Rouge in the late 1990s/early 2000s named Derrick Todd Lee. However, when Lee was killing in/around Baton Rouge there were two other men also killing women in the Baton Rouge area - Jeffrey Lee Guillory & Sean Vincent Gillis. When Lee was caught, it received a lot of media attention and many people went back to feeling safe, not knowing Gillis and Guillory were still out there (they were arrested in years to come). Before Lee & the others were caught, LE surely had to know that some of the cases of murdered women were related and some weren't (especially since Lee left DNA behind) but they didn't ever let on that it was more than one serial killer operating...probably so residents wouldn't get even more panicked (a friend who works in local LE has told me they did indeed know there was more than one SK operating in the city but they didn't let on).
I hope LE on LI knows more than we know about whether or not the cases are connected (but with the UID bodies, who knows), but I wish we had more info. The Baton Rouge example leads me to believe there may be at least two killers working/dumping bodies in the same areas on LI.