With regards to being unaware of a particular ruling in Islam, is one excused from previous misdoings? For instance, I think I had mistaken purity after menses a few years ago and prayed but then later discovered otherwise. I might’ve prayed some Salah with invalid ghusal so would I be excused from making them up. Jazak Allah, may Allah reward you immensely. Kindly keep us in your prayers.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.

You have not clarified what you did specifically so that we may issue an appropriate ruling. However, if we assume that what you said is correct, we say that scholars disagreed regarding the person who misses a condition or a pillar of the prayer out of ignorance of its obligation, as what happened in the case mentioned in the question. The majority of scholars hold the opinion that making up for this prayer is obligatory, but Shaykh-ul-Islam, Ibn Taymiyyah held the opinion that making up for the prayer (in this case) is not obligatory, according to a narration reported in the schools of jurisprudence of Malik and Ahmad. He provided evidence from many Hadiths, such as the Hadith tackling the man who prayed badly (in the presence of the Prophet, sallallaahu 'alayhi wa sallam, and other Hadiths, but the Prophet, sallallaahu 'alayhi wa sallam, did not order them to make up for their previous prayers. You have the choice to follow Shaykh-ul-Islam in this regard and not to make up for those prayers.

Allah knows best.