Wasn't there some talk quite a while back about the Spring/Summer months and the perp maybe visiting the LI area? The fact that Valerie was last seen spring/summer, I think is significant in this somehow.
My cousins have a house in Gilgo and only use it in the summer months. That actually could make a lot of sense that the killings would be happening when he was around in the summer months if he in fact was summering on Long Island and if he came yearly he would very well be familiar with the area. Another thing to consider is Maybe the killer was traveling from the south. He would have to drive through New Jersey on his way to Long Island and if he made the trip to and from annually he would most like make the same stops on the way back up and down. Could this be the link to AC? The Long Island victims seem to all have gone missing between Memorial Day and Labor Day so If the AC victims were killed before Memorial Day and/or in early fall this could be a great possibility.