Looking under where the button to open the boot/trunk is, I can see the number plate lights. Does everyone else's look like this? They look like they've been pushed in behind the metal body of the car, although they're not loose. Every other example of every other car I can find (although none of them are Prii) the light fixture is attached neatly, and usually flush, to the hole in the bodywork of the car, similar to how the interior light inside the boot/trunk is fitted. Mine have a gap between the light fixture and the hole big enough to stick my little finger in. Pondering the risk of water ingress here too. Pixel 2 ?
It might be ok; here's one decent sized image I could find. For definitive answer (if no one here with a 4th gen checks, posts a pic), swing by a dealership and check against cars on the lot? http://st.motortrend.ca/uploads/sites/10/2016/05/2016-toyota-prius-two-hatchback-trunk.png
It's a little hard to judge from the pic, but it kinda looks like dark shadows, as if it's recessed with a gap. Yeah check out another at dealership.
Mine's the same, recessed by about 5 or 6 mm. I think the lights are mounted in the metal part of the lid, the holes are in the plastic part.