I’ve read that the 1080p blu-ray discs included in the 4k boxed set as well as the individual 4K releases were the new scan, but the individual 1080p discs are now just the old blu-rays repackaged with the new covers. Is this true?
The 1080p blu-ray-only releases were always the 2011 discs repackaged. They came out before the 4K set and releases, and were the first release to have the new packaging. That release was seen to be a backstock-clearing exercise more than anything.
The 4K set and their accompanying 4K individual releases have the same packaging design as the preceding blu-ray-only releases, but they are the only way to get the new scans on a blu-ray disc. You HAVE to buy a 4K release in order to get the new scans on a blu-ray as a pack-in.