I have seen this before with "aftermarket" pads to ensure that they dont squeal, it does look to me that the pads were made like this, someone would have to be very clever to grind that much off, so very neatly!! ~ i dont think they are genuine OEM AP pads and if it was me, i would replace them with the correct genuine ones.
Powerstop Brakes are now part of British Motor Heritage and their MD John Yea has written an article in Motoring Classics and i quote
"" there are too many sub-standard brake parts on the market, and i am particularly concerned about some of the very cheap pads and linings that are sold within the classic sector. It is an old adage that there is no such thing as a "free lunch", and with brake components I'm afraid you largely get what you pay for. In the extreme cheap brakes might not just cost you your car, but your life as well.""
I have also read elsewhere of tests that were carried out using OEM parts and cheap aftermarket parts ~ the wear rate was much higher on the aftermarket parts and the efficiency was lower, making stopping distances much greater. you reall get what you pay for. Buy peanuts and you get monkeys!!!!