I own two P226's. One is an American-made (UU serial number) aluminum frame/stainless steel slide unit manufactured circa 2000. The second is a German-made, DE-stamped all-stainless steel gun manufactured about a decade ago. Both guns have around 1,500-2,000 rounds through them.
The first picture below shows the slide of the German gun. There is an obvious divot above the slide stop cut-out. The picture exaggerates the divot somewhat and it's not as deep as it appears but you can definitely feel it with your fingernail. The American gun has no wear in that area whatsoever.
The second picture is of a German frame/American slide P226ST manufactured in the early-mid 2000's that belongs to someone else. It too has a divot in the same area. A quick google search confirms that this is not an uncommon occurrence.
Any idea as to what could be causing this wear on the outside edge of the slide wall? And why would this happen on some but not all P226's?