I think this is the whole point of the discussion, and you seem to be dodging the hard parts. How fuzzy is acceptable? Do you suggests you want to pick the herd of all possible Ah-Chens? How would you define what all possible means? Where do you draw the line between those and someone else?

If I'm reading So8res correctly, he doesn't particularly dodge the hard part.

At a timepoint X, which is when she fell sick or some other schelling point for avoidance of fatal illness, there exists a vector matrix/machine state of all the interactions that, at that point in time within the reality observed by this Shen, together are the essence of the {computational process} that this Ah-Chen was then, along with all the possibilities and movements there.

So8res!Shen wants to copy that particular set of computational process state vectors and transplant it into a different point in spacetime, on a medium (functioning human brain within functioning human body, preferably) that is sufficiently similar to the old one to hold at least the same computational instructions that led to that Ah-Chen-state.

The copied state of interaction vectors encodes all the possibilities of then-Ah-Chen's future, yet will play out differently as per a not-exactly-identical environment and different "flows of the Tao". One of those environmental differences is, as per the request specifications, that the body housing the brain on which she is then computed is not fatally ill.