There are several stories how the prayer was written and how it came about-point is, supernatural revelation was given to the successor of Peter and is rather timely, in lieu of rising Modernism and als, telling why certain people had it dropped after V2....
as far as the source, too many sedes are trying to set back that vacant chair, so I find it questionable....mark my words, in the future, there will be a split in SV circles, with more people like CM/Raoul and setting the vacant chair farther and farther back in time......until, well, nothing is left.....