Looking ahead to the Feast of the Assumption, I noticed that in the Graduale Romanum and the 1961 Liber Usualis (the one on the Musica Sacra site), the Propers for Mass that day are:
Int. Signum Magnum
Gr. Audi, filia
Al. Assumpta est Maria
Off. Inimicitias ponam
Com. Beatam me dicent
But in the Chants Abreges on the MS site, as well as in a copy of the Liber I have from 1938, we have these:
Int. Gaudeamus Omnes
Gr. Propter veritatem
Al. Assumpta est Maria
Off. Assumpta est Maria
Com. Optimam partem
Yes, new propers were introduced when Our Lady's Assumption was dogmatically defined in 1950. I haven't researched whether they were newly composed or why that was done.
For a TLM (1962 Missal), a schola director needs to make sure everybody has the post-1950 propers. For the post-Vatican II Mass, either version may be an option, at least for the Introit.
For feasts introduced for the hundred years or so before Vatican II, there seem to have been new propers provided, whereas since then, there seems to be more use of commons or re-use of chants. For instance, the propers for the Feast of Christ the King, which was introduced in the 1920s, were newly composed or adapted. I guess the thinking is that the old chants are part of the authentic repertoire, but the new ones are not. Wasn't there some discussion along these lines a couple weeks ago about propers for Feast of Sacred Heart?
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