@stoveliker already gave an excellent answer, but just to add to, augment, or even re-enforce what he has already said:
Of course there must be some dependency on cords burned, it seems unintuitive to expect anything else. But real-world experience has run somewhat contrary to this, if we are to give any merit to the anecdotal evidence posted to this forum over the last decade or more. Owners seem to be showing much more dependency on hours than cords, with
@Highbeam and I probably representing the most two extreme ends of the spectrum.
Case in point, I'm putting about 7 cords of very high BTU cordwood (eg. almost exclusively oak for 5 years) thru one Ashford 30.1 every year. I don't remember Highbeam's numbers exactly, but I think he's somewhere around 3 cords per year of low-BTU softwoods, thru a Princess. My combustor is more than 4 years old, and while obviously much less hyper-active than it was when new, it's still doing a good enough job in my application. Highbeam sees black ooze dripping down his chimney if he pushes his combustors past 2 years. Clearly, it's not only about cords.
But when we look at hours, I think him and I are actually running pretty similar hours. I start around Oct.1, and am often still doing evening fires up to June 1, although I honestly start to get pretty lazy about lighting stoves by early May most years. I think Highbeam's season is of similar length, yet he's ripping thru at least TWO combustors for each of mine.
So what's the difference? I once accused him of just being more picky than me, but he made it pretty clear that there's no "maybe" about when his cats die, the "black ooze" comment wasn't an exaggeration. So, it seems his application using softwood at low-BTU output rates must rely much more heavily on having an ideally-functioning combustor. In fact, I'd be tempted to take one of his spent units, and see how it performs in my setup, to see what we could learn from it. I wouldn't be surprised at all, if a combustor that fails to cut mustard in his setup, works just fine in mine, based on the demands of our individual applications.