That’s not quite right. In the mid nineties the film was physically and the color photochemically restored. Only those sections/elements that required CGI updates were scanned at 2K, reworked, and then film outs were created that were inserted in the restored negative, replacing the original shots:
http://fd.noneinc.com/secrethistoryofstarwarscom/secrethistoryofstarwars.com/savingstarwars.html
The 2004 release was based of a 2K scan of the negative, while the 2019 release is based on a 4K scan done in 2012.