you cant drill toughened glass!!! its whole design is to break into small pieces when it has an imperfection- so you drilling the hole will create an imperfection- booom

if you dont believe me- touch an angle grinder on a piece of car glass and i bet in no longer then 10 minutes its gone booom

Saxo rear windows are drilled for the hinges to screw into.

the glass is drilled prior to the toughening process not after

I think I'd want the hinges secured to the glass properly. If they're stuck on, the hinge will lock them closed but a sharp pry with a screwdriver would probably lever the glass off the hinge.

My Mum has these on her 206 and they're pretty useless tbh.

Actually if they were stuck to the hinges you'd have the added problem of getting them to close tightly enough against the seal to be watertight without the hinge coming unstuck as you fastened the window shut.