As late as the early 2000s! I was still setting up IPX for some older DOS/Win95 games to play over the LAN as recently as 2008, and my Novell class (last one offered at my college, around 2007) cited several large local companies who were still employing that technique as a “security through obscurity” thing, though the professor was mainly just citing use cases for IPX rather than promoting new implementations of it.