There's a Snoop Dogg interview where he makes an interesting point about this. Apparently, after 7 years, an artist has the right to reclaim ownership from the label by remastering?
This is essentially what Taylor Swift is doing with her Taylor's Versions. After being ignored when she requested to buy her masters, she essentially did a "Fine I'll do it myself" and is now remastering all of her old work.
Correct. The royalties structure in music has the 2 parts - composition and performance. If you own both, you get 100% of the royalty from all those sales/streams.