While you are 100% accurate about when "personhood" begins (being Philosophical), we do know that premature babies as young as 24 weeks of gestation have been born, and survived. Would you at least say that was at least one likely boundry of "personhood"?
The problem is, that the Blue State abortion fanatics refuse to establish even a baseline, because they know that once that line is drawn in the sand, it can be argued for movement. They refuse to even define the line in the sand, because they are just as fanatical as the Red State crowd on this issue.
Making it about Red State anti scientific types, when it is much more nuanced than that, is a disservice to the discussion.
Here is my suggestion for "personhood", legal scientific accurate. Personhood starts the moment the fetus (baby) is able to survive outside the womb. We know when that is, because we have proof via example.