I wish that there was a tag for "Chant books: other Solesmes".

(Tagging @Charles_Weaver in advance!)

Matthias Bry is working on a practical edition, semiologically-informed, of the Nocturnale Romanum for Matins (he aims to prepare the book for the Divino Afflatu rubrics as well as 1960).

He recently visited Solesmes, and he found this gem from 1920 in the archives. (All of this is copied from his comments; Matthias is so busy with his various commitments that writing this up again is impossible.) Dom Jacques-Marie Guilmard pointed Matthias to the box when he inquired if Solesmes had ever worked on a nocturnale.

Only the Psalter, Common tones, and Advent were made before the project was archived.
A large portion of the Psalter was published in the 1922 editio typica of Holy Week, which has the Matins of Monday, Tuesday and Wednesday in holy week which are just ferial Matins.

He adds:

There is also correspondence between Dom Mocquereau and the S. C. R. on the topic. Looks like a burst of typesetting efforts was made from the fall of 1915 to the summer of 1916, and then from winter to summer of 1920. Hundreds of comparative tables for responsories are joined, probably established in the meantime from 1916 to 1919.

Unfortunately, why Dom Mocquereau felt compelled to abandon this is not clear from what Matthias saw so far (just the scores) ; I note in passing that they were at work on the Christmas book among other projects, as well as reestablishing monastic life at Solesmes, which only occurred in 1922.

Most interestingly, Mocquereau (or someone in his orbit, at Solesmes or in Rome or elsewhere) believed that the authentic tone for the mode VI invitatory was the one with Si-flat found in Matins of the dead. However, this view was not universally shared when the Liber Hymnarius was produced, though that is now changing in French musicological circles; Dominique Crochu is in fact working on scores for the Nocturnale project.

One striking feature of this page is the use of the 6a invitatory tone with flat si, aka the tone "pro defunctis", that was deemed "inauthentic" during the preparation of the 1983 Liber Hymnarius, from which it is absent. Crochu, Gapsys et al are of the opinion that it is actually a very primitive ferial tone. Apparently, either Mocquereau or someone at the TPV was also of this opinion.

I also find it striking that Mocquereau wanted to see things on a page; he was not concerned with rhythmic signs at this stage, and although it's hard to say how far he would have gone, perhaps he would have introduced a special oriscus more widely had they needed to publish all of the responsories and not just the most common ones needed sooner rather than later (Christmas, Tenebrae, Easter, Pentecost, Corpus Christi)