What is the ruling regarding previous prayers in which the final Tashahhud was not recited? Do they have to be made up, given that their number is not remembered, or can they be compensated for by two prostrations of forgetfulness?

The Tashahhud concludes when the worshipper says: "wa ashhadu anna Muhammadan 'abduhu wa rasuluh (and I bear witness that Muhammad is His slave and Messenger)." Scholars have differed regarding the obligation of sending blessings upon the Prophet, peace be upon him, after the Tashahhud. Many of them consider it a Sunnah (recommended act) whose omission does not invalidate the prayer, while the Shafi'is and Hanbalis consider it obligatory in the final Tashahhud. We incline towards the view that it is obligatory as a precautionary measure. However, many scholars permit issuing a fatwa based on a less preferred opinion after an act has occurred and it is difficult to rectify it. Some scholars also hold the view that whoever omits a condition or a pillar out of ignorance is not required to repeat the prayer. Therefore, your past prayers are sufficient, and you are not required to repeat them.