"The story starts in 1507 & the events chronicled in the ballad
were supposed to have taken place in the summer of 1510"

It's a convincing story as you tell it, Joe. I would also be interested in your source. I would also not be disappointed if you can't find it, because, whether the ballad is founded on real events or not, we still have the ballad and its myriad tunes in their myriad forms.

This interesting page
http://www.maybole.org/history/books/CarricksCapital/countessandgypsy.htm
quotes Chambers, who goes with the 6th Earl.