What Eric said and know that as the cog counts increased the clearances are reduced. As Shimano became the 500 pound gorilla their dimensional requirements became the frame designer's (and builder's) standards. But for each change of drivetrain version those standards also changed. Additionally not every bike brand would follow those standards even as they existed for the bikes that were being made for the components that were speced on their new models.
I would want to have the bike in hand but a few file strokes will likely create more chain clearance. I'd want to be sure that only the stay end and the brass filler was being removed and no hole into the stay's interior was likely. Andy
Shimano Framebuilder Info - Pvdwiki (peterverdone.com) Here's an example of those standards from over a decade ago. Current stuff have "new and improved" guidelines
