I have always thought that the bare shank left behind the eye on a classic Catskill dry was for the use of the Turle knot. However, in reviewing some knots I noticed that many of the most popular FFing knots of the 1940's were of the jam type behind the eye. The advantage of such knots is the tippet comes straight from the hook shank, forcing the dry fly to cock properly on the water. Other knots, which are not fastened behind the eye, can pivot anywhere on the eye.
Here is a selection from "The Field Book of Freshwater Angling", John Alden Knight, Putnam,1944:
Personally, I have always used the Turle knot for up-eye and down-eye flies; but I might try the Wood knot this season.