When I perform Wudhu, when wiping my feet, I usually did not go wipe the way up to the joint of my foot, I only went half-way. Does this mistake make all my prior Wudhu invalid? (And thus, my prayers/worship)?
Based on obligatory precaution, wiping the feet up to the raised part in the middle of the foot [before the ankle] will not suffice. However, since this is an obligatory precaution, you can refer to another jurist (marja’) in this matter who considers that wiping up to the raised part of the feet sufficient. One of the prominent jurists in the holy city of Najaf his eminence al-Sayyid Mohammed Saeed al-Hakim considers wiping from the tips of the toes until the raised part of the feet -a little bit before the joint- sufficient.
[According to the opinion of Sayyid al-Sistani]