I bet this story is made up. There is no way someone you just found that 90s wax like that at an estate sale
. All kidding aside, it's an awesome find. I love hearing stories like this and it makes me want to keep searching this stuff out.
As for the grades on your Mantles, I have no idea. I collect low grade and have only submitted twice for some really obscure issues. If I had these, I'd definitely wait for a monthly special and send the better cards/players off for grading though as I think you'd get much better returns with these in holders.