Long before Pope John XXII made Trinity Sunday universal in 1334, a votive Mass in honour of the Holy Trinity was already in circulation across the medieval West, traditionally attributed to the English scholar and liturgist Alcuin of York, who served at the court of Charlemagne in the eighth century, a text individual bishops, monasteries and dioceses could choose to use on a Sunday of their own selection long before there was any single, church-wide feast day fixed to it, so that the eventual universal feast formalised and gave a single fixed date to a devotional practice that had already existed in scattered, locally chosen form for several centuries.
That gap between an available votive text and an actual mandated feast day is itself informative about how the medieval church's liturgical calendar grew: individual devotions frequently circulated widely and were adopted unevenly by different dioceses long before Rome formally universalised them into a single fixed date binding on the whole Latin church, a pattern this atlas notes elsewhere in the case of Corpus Christi, and Trinity Sunday's own centuries-long gap between Alcuin's votive Mass and John XXII's 1334 mandate is one of the clearer documented examples of it.