Is re-performing the prayers of the day after ghusl from a wet dream, which was only noticed after it had dried, valid?

The inquirer's action is correct and in accordance with Islamic law, as ritual purity is a condition for the validity of prayer. Janabah (major ritual impurity) necessitates ghusl (ritual bath), and a prayer offered without purity due to janabah does not discharge one's obligation unless the prayer is repeated after performing ghusl. If semen is found after prayer and there is doubt whether it was present before or after, the default assumption is that it was present afterwards, and repeating the prayer is not obligatory. Similarly, if there is doubt about the time janabah occurred, whether from a previous or subsequent sleep, it is attributed to the more recent sleep.