The missing lightsaber effects were partly fixed in 2004, then completely fixed in the 4K.
Vader’s lightsaber, fixed in 2004, was redone in the 4K.
This strange instance of new flash frames being inserted to perhaps cover up the tiny Vader lightsaber in the original (instead of rendering a new blade) was redone in the 4K.
The original shot accidentally showed part of the film with the soundtrack on it. It was fixed for the Blu-ray in 2011 by extending the right side of the frame, leaving the TIE where it was in frame. The 4K version extends the left side of the frame, moving the TIE into center frame.
A frame of missing Y-Wings was corrected in both 2004 and the 4K.