You mean the "Sancta Maria, mater Dei" part? Which is the oldest book you know contains it? I haven't seen it anywhere but in 20th century Solesmes books. And, to my (limited) knowledge, in this long form it hasn't ever been used in a liturgical function (as a Divine Office antiphon or in the rituale), but merely as a devotional chant, which would seem to somewhat support the "Solesmes hypothesis".
"Sancta Maria, mater Dei" seems to go back the the 16c. (and I just noticed the full articles are attached to dmarsh13's post). The pre-tridentine settings at CPDL mostly have "Sancta Maria, Regina coeli…"
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