The question of whether an individual at an earlier time is numerically identical with an individual at a later time does not, therefore, have a determinate answer.
The unity among past, present, and future mental states, generated and supported over time by the same body and brain, in weak reductionism is enough to yield the notion of a numerically identical and temporally extended individual.
Even numerical identity would become indistinguishable from absolute identity, if we could not assume different numerically identical
But on the assumption that persons are wholly material, persons are numerically identical
with their bodies.
If, however, one's original body ceases to function while the cerebrum transplant takes, one "wakes up" psychologically continuous with oneself before the operation, but one is not numerically identical
with oneself before the operation.
Likewise, an entity's potential for personhood is strong only if the entity is numerically identical
across time with any actual person who realizes its potential.