Just as a point of reference, the master for the 1980 AC/DC concert film "Let There Be Rock" was said to be lost for the longest time, only existing on VHS and possibly one or more worn-down release prints.

It was released on DVD & Blu-ray this year, fully restored from the original negative. The explanation?

The guy who shot the film refused to allow a release scanned from the negative which he possessed. His rights to it just recently expired.

So you never know what the heck's going on behind the scenes...