They can be very very close. Here’s a link to a video from the guy I mentioned. I don’t know if there’s a way to link directly to the spreadsheet, but it’s in the description.
And to emphasize your point, the filtration can’t really work without the fit. It doesn’t matter what number comes out of a test of the mask if you can’t comfortably wear it without it leaking.
He also talks in this video about all the fake masks out there. Amazon, eBay and Etsy are all pretty much impossible to tell if it will be genuine. (So probably safest to assume not.)