Toei hasnt lost any film master. What do you think they used to make kai and Funimation’s film prints with?
What they dont have any more are the audio masters for any of their old series cause it was a common practice to reuse the magnetic tape again to save money and space. Only a couple of old toei anime releases have proper audio releases, the compilation films of Fist of the north star being one of them.
There was/is a very large project of gathering videotapes which have recorded the original broadcast audio from tv stations for Dragon Ball and Dragon ball Z.
Also on the 480 releases, its just toei not caring about their products. Do you think a company that actually cares would allow funimation to release a 30th anniversary of their biggest series not to mention with such an awful quality?