In a decree (1759), Clement XIII ordered the Trinity Preface to used on Green Sundays. This supports a strong case for the naming of these Sundays per annum in the old English (and North European) way as Sundays after Trinity.
I draw attention to several points.
The modern emphasis on Sunday as a weekly minipascha is true but too narrow. As Clement XIII's document points out, Sunday is also the day of the Creation of Light; indeed, of the beginning of Creation. And also of the Resurrection; and also of the Pentecostal gift of the Spirit. And thus of the Holy Trinity.
The same Magisterial document refers to the traditional use on these Sundays of the Quicunque vult. I believe, and have written before on this blog, that the disuse of this Canticle (since the corruption of the Roman Rite really got under way under Pius XII) is one reason why even some clergy don't really seem to have any sense of the Trinity, as defined by Mother Church, any longer - they are, it sometimes appears, modalists. The fact that when the clergy of the English Ordinariate were being 'formed', a lecturer assured us that the QV was "heretical" is a disgrace which still stimulates my indignation.
It also reminds us of the antiphon which usually came towards the end of Sunday Mattins: "Two Seraphim cried one to the other *Holy Holy Holy Lord God of Hosts, *All the earth is full of his glory. V Three there are who bear witness in heaven, Father, Word, and Holy Spirit: And these three are one. Holy ... Glory be ... All ...". This lovely text, of course, draws upon the verse in the Vulgate and the Authorised Version (Patrimony Patrimony) in I John; commonly omitted in modern Bibles including the Neovulgate because of its extremely weak attestation in Greek mss..
We need to become very much more robust in embracing the Scriptures as the Church has handed them down to us rather than making an idol of the methodology (with its underlying conceptual assumptions) of Westcott and Hort. (Even in WH terms, I think one could make a case for this verse having been omitted so widely because of parablepsis due to homoeoteleuton.)
We need a reacceptance of a more holistic sense of Tradition ... and a recommitment to the noble crusade of rolling back the 'Enlightenment'.
And finally: Clement XIII, in the actual words of the Decree itself, refers to the use of the Trinity preface on Green Sundays and says "inde a [not 'in'] vetustissimis temporibus in usu fuisse dignoscitur".
In other words, the Holy Father does not say: I've had a perfectly spiffing idea; let's do so-and-so. He bases what he decrees on Ancient Tradition and Precedent. That is very significant. It is the immemorial Roman instinct for preservation and continuity. We need more of it. Especially in Rome. Not least in the Casa Santa Marta. I wonder if the Quicumque vult has ever been chanted in the chapel there.