Hi there,
So i think take a look at the Technical reference guide for the Nrf52 part. I’m sure it is addressed in there, the other is using the Flash memory to tell the boot count and if it is awake, Also there is a wakeup Stub that runs a certain setup stub when waking up, AFAIR
also, You wouldn’t know if the advertisement is seen or not too that way I would look for another method with a Notify or some feedback, that way you can maximize your sleep counter and not wake premature to being required to (sensor update or x?). if that makes sense
HTH
GL 
PJ 
All of it is GOOD stuff 