Windham claims that their Chair A, all by itself, is 1550 feet. (The remaining 50 feet would probably be the run-out down to the lodge.) So this is a difference that can't be accounted for by MountainVertical's methodology.
Interesting that the SAM Magazine listed the Windham 1993 HSQ install as 1320 vertical feet. These lift Installation numbers from SAM are usually very accurate.
At Hunter, I am guessing that MountainVertical used the AA chair, top to bottom. The remaining 80 feet probably comes from Hunter One, which I think is at a lower elevation, but isn't part of a continuous run down from the top of Hunter West.
Here is the Hunter Mtn 1987 HSQ installation which is listed as 1471 vertical feet by SAM Magazine.