I'm not personally convinced that eliminating the Marian tone (and others) necessarily follows from the rubric to not change doxologies (in the 1960 Breviary reform), but it looks like the editors of the Liber Usualis in the 60s thought so.
The rest of the melodies mentioned on p. 269 will no longer be used, as well as that given for feasts of Our Lady, p. 1256.
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