Presumably when A gets cancelled, he comes by and says, "A just got cancelled" (or you tell him, depending on how news flows). "This was part of my plan for this cycle, how can we adjust the plan?" And then you discuss giving him proper credit for work on A until it was canceled, and then break down what his new priorities look like.
Or, "I just started work on D, how does this fit in the plan?" "Currently it doesn't, but lets get it in there".
There should be very few things that happen that would be so important that they'd be worth discussion in a promotion that you don't communicate about within a day or two of it first appearing on the radar (if not hours).
The last issue of a reorg is the one that is toughest to deal with. I would talk to their new manager, layout their plans, etc..., but there's no guarantee that the new manager will have the same philosophy.
Being a manager is hard work. And frankly, I'm largely done with people management. It's the hardest job I've ever had, bar none. But its important, and I think some of the problems noted in this article are things good management training can deal with.
Basically if you have a formal appraisal process at all you're trapped in a machine.
"Sorry, corporate priorities changed. A and B were cancelled and C was put on indefinite hold. Sure, you did great work on D and E, but those weren't part of your stated goals for this year. Oh, and by the way, there was a re-org and the manager who promised you a promotion isn't your manager any more."
Not saying you personally do that; it sounds like you're a pretty good manager. But I've seen this pattern many times, and know a lot of other people who have experienced it.