technically, that “1” on the back side looks more likely to be on the header that runs the side rather than the GXP. If it’s meant to be the GXP header, then it should be rotated 90*. And if anyone cracks open the board files to do that, also just add the same, or a dot, on pin 1 on the top.
The board should be marked of course so you plug things in correctly but the real issue here is that the documentation should have this information in the first place.
I prefer to mark the pin 1 with a small CIRCLE on the board if there is no room to place any numbers. Easier to see too.
I also prefer to make PIN 1 SQUARE and the others are all round.