I have recently learned new information about najasat. This information was available and exposed to me before however I didn’t realise the importance of a small detail from it until now. With this new knowledge that I’ve gained, I wanted to know if my previous prayers will be accepted in my previous state of najast or if I should count those as qaza prayers?

If you are aware of the existence of impurity, and you know that prayer is not valid with it, but you neglected purification, then you must make up for it.
But if you are ignorant of the invalidity of prayer, and you are excused in your ignorance, then it is not necessary to make up for it