In the unpublished Mary Missal fragment to which I referred on July 26, the Eastertide Mass of our Lady has a Sequence which neither the late Walter 'Patrimony' Frere nor I were able to find elsewhere. I print the remains below;  indicates a hole in the manuscript. James 'Patrimony' Bradley kindly spotted that the first stanza came from the Mariale (III) of Bernard of Cluny; a long praise of our Lady in 15 Rhythmi; and the other stanzas are scattered around in V. I was accordingly able to fill up most holes in the text from Analecta Hymnica Medii Aevi; Volume 50, pp 423 sqq...
This hymn is associated with the name of S Casimir, because a text of it was buried with him. We know it best in the form of the translation Daily, daily, sing to Mary, which only uses a small selection from the hundreds of stanzas. We sing it regularly at S Thomas's; my motive for selecting it is that it is pretty well contemporaneous with our patron S Thomas.
The question remains, whether the centonisation was done by Bishop 'Patrimony' Grandisson of Exeter, a great client of our Lady, for the Mary Missal which he had made for his Cathedral or for his collegiate foundation at Ottery; or whether someone had already done the work.
At the bottom, for my own satisfaction, I give, from AH, a brief account of textual variants.
III.15 [O beat]a
per quam data
nova mun[do gaudia]
regna sunt caelestia.
V.19 [Quot dolore]s
tua sensit anima
cum in cru[cem
gens levavit pessima!
21 Corde tris[ti
28 Sed quam laeta
die statim tertia
[cum rex fortis
30 Nec nar[rari
tuum possit gaudium,
pacis dedit nuntium.]
mss=most of the manuscripts; ms=one or few of them.
III.15 ms quam beata
V.19 mss quot angores quot dolores; ms tot dolores; ms et dolores; ms quot languores quot dolores; ms quot dolores quot angores
mss cum; ms dum; ms levavit impia.
V.21 mss tuum cernis filium; ms cernens filium; ms tuum vides filium
V. 28 mss o quam; ms es completa; ms et repleta [haec cum assonantia]; mss die facta tertia; ms die virgo tertia; ms facta die tertia; ms dum rex; ms qua rex; ms dirae mortis; ms pertulit; ms iudicia.
V. 30 mss quis narrare quis pensare; ms quis pensare quis narrare; ms hinc narrare, quis pensare; ms unde maestis; ms quoniam maestis.