Canon  1087 Those in sacred orders invalidly attempt marriage.

Canon 1108 §1. Only those marriages are valid which are contracted before the local ordinary, pastor, or a priest or deacon delegated by either of them, who assist, and before two witnesses according to the rules expressed in the following canons and without prejudice to the exceptions mentioned in cann. ⇒ 144, ⇒ 1112, §1, ⇒ 1116, and ⇒ 1127, §§1-2.

Thus ends your assertion that "The RCchurch does NOT presume to pronounce upon the validity of a civil marriage entered into by an ordained priest."