It has indeed happened.
https://boingboing.net/2018/09/05/mozart-bach-sorta-mach.htm...
Sony later withdrew their copyright claim.
There are two pieces to copyright when it comes to public domain:
* The work (song) itself -- can't copyright that
* The recording -- you are the copyright owner. No one, without your permission, can re-post your recording
And of course, there is derivative work. You own any portion that is derivative of the original work.
Right, that's my point... I can sue anyone for anything, doesn't mean I'll win.
You cant sue if you dont have money, a big corp can sue even if they know they are wrong.