What is the ruling regarding making up Dhuhr, Asr, Maghrib, and Isha prayers, or only Maghrib and Isha prayers, when blood [menstrual or post-natal bleeding] descends after Maghrib and the exact time of its descent is not precisely known?

If you did not pray Dhuhr, Asr, and Maghrib until after Isha, then you are sinful and must repent. You must make up these prayers, assuming you were pure at that time, because purity is the default state. The blood you saw after the Isha prayer time began is attributed to the nearest time, which is after the Isha prayer time began. You should also make up the Isha prayer if you managed to perform the takbirat al-ihram while pure before the onset of menstruation.