Per an extended conversation with Apple today:
AppleCare for iPad covers a Pencil purchased with the iPad. But if you exchange that iPad for a different model, and keep the Pencil that was purchased with that first iPad, your previously-covered Pencil stops being covered by AppleCare because it wasn’t purchased with your current iPad.
Apple can fix that, but you have to get their phone support people to take care of it. It’s not automatic. And I’m not sure how far down the road they’d be willing to deal with it.
I would presume this applies to the folio keyboard as well.
So…if you’re swapping an iPad out, make sure you get the extra coverage on your accessories sorted out. 