I have just noticed that Forum Auctions have a calendar in a forthcoming sale (28 September, 2023, lot 24), with a short description and a two-page opening reproduced in the online catalogue (shown above).
The description tells us that it is a six-leaf quire, bound in "19th century vellum-backed marbled boards", which suggests it was removed from its parent manuscript at least a century ago.
In fact, a look at the entries in the two reproduced months, February and March, allow us to determine that it comes from a volume that was still intact when sold less than a decade ago, at Sotheby's on 8 July 2014, lot 54. [archived here and here]
The Forum description mentions the feast of St Herculanus, bishop of Perugia, who appears at 1 March:
A few lines lower down, however, not mentioned by Forum, is "Consecratio ecclesie sancti Juvenalis episcopi et martyris", added by a 17th(?)-century hand on 4 March, suggesting that the manuscript had moved by that date to Narni, where the cathedral is dedicated to the local bishop-saint, San Giovenale [Wikipedia]. The Sotheby's description also records an "inscription of that date: “Breviarium Cathedralis … cum lectionibus S. Juvenalis episcopi et martyris” at head of fol.1r"
This is an instance where one can find additional provenance information by tracing previous catalogue descriptions; in 2014 it was recorded that the volume included the armorial bookplates of John Perceval (1683-1748), Earl of Egmont, and Richard Caton (1842-1926), Professor of Physiology, and Lord Mayor of Liverpool 1907-08.
I viewed the 2014 auction and annotated my copy of the catalogue. I noted that there was a loosely-inserted card, printed "Ecclesiastical Art Exhibition | Loan Collections | No. in Catalogue [with "430" inserted by hand] | Do Not Touch". The last line suggests that this was the actual exhibition label, and that the manuscript was not exhibited behind glass in a vitrine. I have not seen a copy of it, but I suspect that if I were to consult the catalogue of the Church Congress Exhibition, 1904, held in Liverpool, I would find that the manuscript had been lent by Richard Caton.