According to the book Versus Psalmorum et Canticorum available on the MusicaSacra website, the additional verses for this Introit are not the ones immediately following the one given in Graduale (Ps. 102:2-5 given above), but verses 21-22 (see attachment), which make particular reference to the angels, as is appropriate for the feast.
Additional verses for the Introit Benedicite - from Versus Psalmorum et Canticorum.pdf
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