relevant links
https://pastebin.com/QnJVhmex
https://gist.github.com/cqfd/ffbdebbbcd3460ec822c3e63572cc282
https://discord.com/channels/889577356681945098/889702325231427584/918625031209246751

tl;dr there would be different code for PDAs owned by the deriving program vs PDAs owned by the system program

willing to fund this issue or any other issues ive made

cqfd (alan) 
Today at 10:59 PM
If there's data on the account then it's definitely not owned by the system program (if owned by the system program then it's "easy", otherwise hard)