I fail to see how they can guarantee it’s the first install.
I game inside a VM with GPU passthrough and I’m pretty sure it would be trivial to install-bomb any game to rack up install numbers and costs.
Moreover, would anyone even trust any number of times Unity tells you your game was installed?
They could a magical 10% that would be hard to prove/disprove.
Anyone with a half-competent legal team would stay the fuck away from any of this nonsense going forward.