For those who are interested in the copyright status of the Liber Usualis and the Graduale Romanum: the US Copyright office finds no renewal, which thereby places the books in the public domain. Here is the letter to that effect.
I guess we could have known this since publishers have already re-printed them without any printed copyright claim but their proprietary interests have kept them from making this public knowledge. The CMAA, however, has no such interest at stake.
This public-domain status does not affect any new material in books published by Solesmes. I'm thinking here of the new version of Ubi Caritas, for example, or the new hymns in the Hymnarius.
As for old material, musicians are free to make copies for weekly worship aids, journals are free to print them as they see fit, publishers are free to re-publish them even at a profit, bloggers can upload them, and webmasters are free to make them available for one and all.
This might seem obvious to most people, but I've heard more urban myths on this subject than you can believe. I've heard Solesmes owns them all, that they own the ictus and episema, that Desclee is still in business and guards them, that they belong to the Vatican, that only 19th century pre-Solesmes editions are available, that Solesmes charges big bucks for printing them, and on and on. Make up any rumor on this subject you want: someone has already beat you to it.
But the thing about copyright is that it is not complicated. The Copyright Office agrees to protect a piece of work or it does not. It has very clear rules concerning what is protected and what is public domain. They are willing to search any title for a fee (and this search was more costly than most because of its international nature and longevity). And they are willing to tell anyone whether such and such work falls under the law.
In any case, the results seem to accord with our intuition about the status of the chant: it belongs to the whole world.
Addendum: In response to a question, here is more detail:
In response to the question about international issues, the US has had an agreement with Belgium since 1887 to respect each other's copyright law. The agreement relevant to France is here but it does the same thing.
As for the Meinrad claims, note that Meinrad (in a passage that might have been written in the early 1990s) doesn't concede Solesmes's ownership of new neumes but only agrees to comply with Solesmes's request:
"As noted in the original introduction, the Abbaye de Solesmes claims a French copyright of certain newly designed notes and has asked that we not reproduce them: i.e. the oriscus, the augmented punctum (up and down), the apostropha and the augmented apostropha. In addition, Solesmes claims under French law the exclusive use of the following new combinations of older signs: the initio debolis for the podatus and torculus, the use of the small note of the diminished podatus to for the diminished porrectus, and the use of the rhombus to form the trigon. Although one cannot copyright a font under American law, we have withdrawn these designs in recognition of the great contribution made by the Abbaye of Solesmes, and we offer substitutes which were newly designed to avoid the conflict with the Abbaye de Solesmes."
Finally on the issue of the rhythmic signs, Meinrad says the following: "While the pitches of Latin chant belong to the tradition, the interpretation with various rhythmic marks by the monks of Solesmes or by others is under their copyright."
The implication here is that signs from 80 years ago (or so) still belong to Solesmes. Neither Meinrad nor Solesmes provide a legal basis for this claim, and it struck the people at the Copyright Office as untrue on the face of it. Public domain means the whole work, including graphics or signs or punctuation.
If, for example, "The Adventures of Huckleberry Finn" is public domain, the Mark Twain estate can't copyright in perpetuity the period and commas therein. The only exception would be the case of a volume with multiple essays in which only the copyright for only one essay was renewed. But that is not the case with rhythmic signs. Nor was any copyright renewed for any aspect of the Liber or the Graduale.