I would like to find the earliest source containing the Stabat Mater melody on page 1634V from The Liber Usualis, Solesmes, 1961 edition:
If the earliest source is not known, I would like a source before 1961.
I checked the 1896 Liber Usualis (pg 1229) and the 1924 Liber Usualis (pg 1644), but both have a different melody.