What do you mean approved by Pius 12th? Wasn't the changed mentioned in the second post done by John 23?
Pax Vobis justifies his adherence to the 1962 Missal by insisting (whether true or false, I neither know nor care) that it was largely composed under the reign of Pope Pius XII. Though I don't see how even he could stretch such a train of thought to apply to the Ember Days.