The evidence needed to permit an abortion under a rape exception is different from that needed to convict a rapist (whether capital punishment, castration, or imprisonment is the statutory punishment): for the first it is necessary to establish beyond a shadow of a doubt that the woman was raped, for the latter, it is also required that the identity of the rapist be established beyond a shadow of a doubt.
I would think that a properly constructed rape exception would require an evidentiary hearing to establish that a rape had taken place. Alas, we are very far from needing to consider the exact details at this point, even though a pro-life policy with such exceptions should garner majority support among the populace (unless the no-exceptions folk let the perfect be the enemy of the good and perversely side with the pro-abortion folk because they can’t get everything they want).
At the same time we could have error ~ after all, we are going to execute the rapist so we certainly don't want to get the wrong guy.
We already have very high standards when it comes to capital crimes. So, let's say "they" (Officialdom or whoever) goes ahead and kills the baby ~ and ends up not able to prove that a rape occurred, or that the accused rapist is the real rapist.
We turn the guy loose, and he moves back in with the woman.
I doubt we want a system like that which rewards duplicity.
Only way around the problem as I see it is that we have to let the rape case play out to the fullest even if it goes beyond 9 months ~ and simply forestall abortion until that rape case is finished.
At that point we might substitute infanticide for abortion to get the same result ~ that is ~ no baby.
I am sure there are those who would love that ~ most likely the people who demand the continued high maintenance of the most exacting standards in capital cases.
The conclusion is that with abortion prohibited EXCEPT FOR the rules for EXCEPT FOR will need to avoid tracking down people in their 40s to kill them because some TV show did a "cold case", and we will also need to avoid letting the anti-execution people get involved.
Maybe we could disenfranchise them entirely. Remember, the EXCEPTION is saying that rape is a serious enough crime that we can execute the baby, and that right there certainly justifies, at a minimum, the execution of the rapist, even more so if we begin engaging in legal post partem abortions!