I'm not falling foul of my statement by not testing every possible variable. That wasn't what I said, read what you quoted and then you'll see that is something different entirely. Maybe. But then again you haven't already so perhaps not.
I tested standard and non standard CZ, BSA, LW, Steyr, Walther and AA barrels in 3 different rifles with 3 different loading mechanisms using JSB Express, Exact and AA Field Pellets, and none of them sealed.
Pellets don't seal completely. QED.
There is the possibility that a pellet seals in a PCP with a certain pellet somewhere in the universe. You're welcome to go forth and experiment to find that possibility. The significance of that finding would depend on the amount of occurrences of that happening with combinations that people whom were interested in accuracy and precision were actually using.