The boundaries between present-day people and non-people can be sharper, by a fiat of many intervening class members being nonexistent, than the ideal categories.

Fair point.

More to the point, a CEV-based AI has a potentially different definition of 'sentient being' and 'the class I am to extrapolate'. Theoretically you could be given the latter definition by pointing

Mm. Theoretically, yes, I suppose someone could point to every person, and I could be constructed so as to not generalize the extrapolated class beyond the particular targets I've been given.

I'm not sure I would endorse that, but I think that gets us into questions of what the extrapolated class ought to comprise in the first place, which is a much larger and mostly tangential discussion.

So, fair enough... point taken.

In other words, except for chimpanzees, cryonics patients, Terry Schiavo, and babies who are exactly 1 year and 2 months and 5 days old, there isn't much that's ambiguous between person and non-person.

Slightly offtopic, but doesn't that assume personhood is binary? I've always assumed it was a sliding scale (I care far less about a dog compared to a human, but I care even less about a fly getting it's wings pulled off. And even then, I care more than about a miniature clockwork fly.)