Apologies: I begin with the assertion of a fairly self-evident truth which I have asserted before; but which seems so counter-intuitive to a modern Catholic that many find it hard to assimilate:
No Pope did, because no Pope could, issue world-wide or general mandates regarding Liturgy before the invention of printing (in the middle of the 1400s).
I suppose that a fanatical uebersuperpapalist could argue that, nevertheless, the power to do so was tacitly incorporated in the Lord's mandate to S Peter, designed to lurk there unrecognised until, a millennium anda half later, the technological moment arrived for it to spring into action ... but, frankly, that is a theological fantasy-world whose sci-fi games I feel little interest in playing.
But there were people who had views about Liturgy and Uniformity ... it's just that they weren't popes! The Emperor Charlemagne was one of them. He wanted to establish in his imperium Romanum redivivum the authentic Rite of the Urbs. Here is the description of Dom Gregory Dix of how he embarked upon this policy.
"Charlemagne therefore applied to the Pope Hadrian I, for an authentic copy ... as early as 781. The Pope was a busy man, and irritatingly uninterested in the great project of securing perfect uniformity throughout the West to the rite of his own see. No book arrived, and Charlemagne was forced to repeat his request. At last, somewhere between 785 and 793 the long-awaited copy came. After all this delay the book the Pope had sent turned out to be unusable as it stood for Charlemagne's purpose. Not only had the text been carelessly copied, but the book itself must have seemed to the emperor strangely defective. ... It is perhaps regrettable that history records no expression of Charlemagne's opinion of the Pope or his book when the latter was presented to him after getting on for ten years of expectation."
Yes!! Pope Hadrian was "irritatingly uninterested in the great project of securing perfect conformity to the rite of his own see"!
I don't think he used to stamp around ranting about unicus usus!
To be continued.