Perhaps because I was "brought up" in the Vatican II sect? I have heard about ordinary jurisdiction and supplied jurisdiction, but I never knew that it literally affected the VALIDITY of the Sacrament. I just thought it was an issue of legalities.
You are correct, it is an issue of legalities.
As Mith posted, the law taught at Trent does not mean the sacrament was invalid, rather without jurisdiction absolution simply does not happen. The Church does not want imposters dressed up as priests, or priests who are under censure or whatever to hear confessions. The Church only permits priests that the bishop personally consents to and knows about and grants him the jurisdiction to hear confessions.
My copy of that says:
"Wherefore, since the nature and order of a judgment require this, that sentence be passed only on those subject (to that judicature), it has ever been firmly held in the Church of God, and this Synod ratifies it as a thing most true, that the absolution, which a priest pronounces upon one over whom he has not either an ordinary or a deligated jurisdiction, ought to be of no weight whatever."