I've got about 7 different editions of Farseekers (I have a problem :$ ), I'll check them now...
First ed, Penguin (1990) -
Part I - ObernewtynPuffin (1993) -
Part I - ObernewtynPoint SF/Scholastic (1994) -
Part I - ObernewtynPenguin (1997) -
Part IObernewtyn & Farseekers, SFBC (2000) -
Part ITor (2000/2001) -
Part IOber/Far/Ash Omnibus, Penguin (2002) -
Part IStarscape (2003) -
Part IPenguin (2007) -
Part IRandom House (2008) -
Part 1 - RefugeObernewtyn+Farseekers, Bluefire/Random House (2011) -
Part I - RefugeInteresting. Agree that they probably just dropped the "Obernewtyn" part to avoid confusion with the first book.
Edit: added as much to the encyclopedia entry for Part I:
~Link~Could someone let us know what it is in the 1997 edition?
Edit: added the ones from meisje's list below.