Can someone please explain how this works in practice.
Take Friday as an example:
Pius V Missal: Purification of the BVM, Double of the Second Class. John XXIII Missal: II Class.
Pius V Missal: At the blessing of candles the celebrant wears a violet cope, the deacon and subdeacon violet folded chasubles. John XXIII Missal: The celebrant wears a white cope, the ministers white dalmatic and tunicle.
Pius V Missal: At the prayers of blessing the long conclusion of the orations is used. John XXIII Missal: the short conclusion is used.
Pius V Missal: After the prayers of blessing the antiphon Exsurge is sung folllowed, as we are in Septuagesima by Flectamus genua etc. John XXII Missal: Exsurge etc is entirely absent.
Pius V Missal: After the procession the ministers change into white vestments and begin Mass, as usual, with Introibo, Ps 42, Confiteor etc. John XXIII Missal: prayers at the foot of the altar omitted.
Pius V Missal: Celebrant reads epistle and gospel at the altar in addition to ministers chanting them. John XXIII Missal: Celebrant does not read the epistle and Gospel but listens to them proclaimed.
Etc, etc.
Both Missals have Quo primum printed at the front of them. Quo primum, as noted in thread above says no change may be made, nothing added or removed. So, if it is binding, with the example of just this one day, why are there differences?