Finished brake pads at the back factory?

Hello! For a long time I changed the linings of the rear disc brakes at my Picanto. The reason was that the brake had set itself to the left, which led to a hot brake and high wear. On the left side both linings were therefore already quite far down, but the one on the right side had not reached their wear limit for a long time. This made something visible, which I have never seen before. A part of the lining was missing! On the photo you can see In the case of the lower surface (outside) an edge which runs in about 45° to the direction of the wheels, from there the surface is ground down to about half of the original thickness. The grinding marks are also in the 45° angle, and also the inner surface (above), which is somewhat more worn, shows still slight remnants of these tracks. My left surfaces were so far down that nothing was recognizable of it. Anyway, this thing is not by chance, the precision of the tracks after the m The blocks are still the original ones from the factory, the new blocks don’t have that, and even a colleague and car mechanic has never heard of it. Therefore, my question, knows of you who, why that is? (And since my uploaded pictures seem to end up in Nirvana: There!