The library of congress does have the original prints submitted for the copyright they digitized. What they don’t have is an archival print. Lucasfilm couldn’t provide one because it doesn’t exist, even Fox never had archival prints made. What they did have was a 3 strip backup of the original camera negative made, which had color layers misaligned they never checked it before putting it into storage. Lucas dug it out in the 1990s and found it was useless.
The only archival quality print Lucasfilm could offer the LOC was the 1997 special edition which they refused.
As insane as it sounds no restored version exists of the original 3 movies at Lucasfilm, and no DCP has been prepared for exhibition. Lucas never spent the money for obvious reasons. He spent money on the 3D conversion and the Reliance 4K scan of the Special Edition, which eventually was released as Special Edition 4.0 in 2020 but not in 3D.