Is it obligatory to re-perform past Fajr prayers that were made up after Maghrib prayer over the course of ten years, knowing that their make-up should have been before Dhuhr?

A missed prayer must be made up when remembered and when one is able to perform it. You are not required to make up the prayers you performed out of order, and you are absolved of them. However, you committed a sin by delaying, so you must repent to Allah and ask about what you do not know, for Allah Almighty says: "So ask the people of the message if you do not know" (Quran 16:43), and because the Prophet, peace and blessings be upon him, said: "Why did they not ask if they did not know? Indeed, the cure for ignorance is asking."