Maybe I'm misreading @IRW Bloodwing 's point, but I read that as them saying that SW has more items from tie-in material that were added into on-screen works ("additions"), in keeping with the general subject of this thread, and as direct follow-up to @hbquikcomjamesl 's claim that ST has more tie-in fiction. (ie - "ST may have more, but SW has more things that ended up on screen".)
Granted, I have no idea if that claim is true or not, since I don't read SW novels. But that seems to be the claim being made, at least to me. (Although it is of course possible that I'm misinterpreting.)
Star Wars has, as near as I can tell, more both in terms of tie-ins AND tie-in stuff that snuck into canon.The count on the latter would run into the dozens, easily, if not much more.
Trek has been notoriously stingy in that regard, prior to the modern era. In fact, the PTB made it a point NOT to raid the tie-in stuff (though one or two things did sneak through, like the use of one of the old FASA starship designs on a computer readout in TNG Season 1).