Captains reduced in numbers are permitted to 'displace' pilots in a lower category if they are senior to them. Thus, you'll see 767 F/Os only demoted to S/O A380 as long as they are senior to those S/Os on the A380. This will occur even if that creates a surplus on the A380. Then we do a reduction in numbers on the A380 and those S/Os on the bottom of the pile go to whatever aircraft they are senior enough to get to.
Thus, you can see that demotion creates as many residual training slots as does promotion. It's also way the company really isn't that keen on demoting people as it's a HUGE training cost. They may (and I stress may) decide that it's cheaper to offer a senior 744 Captain a package- certainly won't be 104 weeks- to get him to go rather than face the prospect of multiple residual vacancies as that 744 Captain displaces an A330 Captain who displaces a 767 Captain who displaces an A380 F/O, etc, etc.
That's my reading of it anyway. Happy for one of the more experienced gurus to shed some light. Kremin? Going Boeing?