Horrors of Horrors! "Space Seed" is not available from the menu! The title is there, but when you select it, the DVD shows the sub-menu of "The Return Of The Archons". The only way to watch the Khan episode is by selecting Title 2 manually from your remote control!
Incidentally, this is the second discovery made from my "all seasons of original series" box. The original discovery was that these episodes are edited versions ( on the DVD sets http://dvdcompare.net/comparisons/film. ... 84#overall ) -- from a fineprint on the box, which I'd shared on rewind forums, and which was then reflected in "overall stats" as "This is the 70's rerun edited versions of the episodes."
The Fuel-Cell box that I have was not distributed directly by Paramount, but jointly by ChioicesUK, and I believe the artwork on the discs is different from the regular R2 UK discs.