It's pretty uncommon to see ring lands fail (break) on forged pistons and detonation can't always be seen on the top of the piston, or the ring, with a bore scope or even with the piston in your hand.
There's detonation that causes pitting on the piston, then there's detonation that causes hammering of the pin bush, pin bore and big end bearing.
I agree that flowing the plenum is a waste of f**king time though. What kind of BS is that? Seriously