HI,
yes they (Ng Ying Kuen and Ng Hang Kuen) are two separate sets:
(
http://www.hunggarkungfu.de/formen.htm)
according to my sifu, Sap Ying Kuen was "made" by LSW by connecting the two, however some shortening was made to them in this transition. In our school the two forms are teached separately first.
unfortunately i am not even close to learning these forms yet, so no more info on the differences...