Proof by Contradiction
I called 331 days out for a Y seat to HNL. I was the first to call, as no seats had been opened up. I was placed on a priority wait list (sounds so catchy!) as a PM. Therefore, if an N-class seat ever opened up for 30,000 miles, it was going to me. I sat on the waitlist and didn't clear the day of departure.
Conclusion: There exists (or existed, more precisely) at least one flight where no SkySaver inventory was allocated for an N (coach) award.