The 2004 transfer was a 8-bit RGB scan of the original negative done by Lucasfilm themselves.
On http://www.rmwusa.com/#start there is even a HD video called "Image Processing" which showcases clips from movies they worked on and to me it looks like that the Star Wars scenes are not taken from the 2004 Master.
It looks like a new scan to me.
I didn't know it was done at 8-bit. Yuck! That's barely OK for LDs.
This one was done at 4K/16-bit.
I'm sorry, i just checked the interview with John Lowry from 2004 about the DVD Release and it wasnt a 8-bit scan it was in fact a 10-bit scan. My mistake.