Thus saith Fortescue: "By universal Church law, in all cathedral and collegiate churches the ceremony of sprinkling the clergy and people with lustral water should take place before the chief Mass on Sundays."
It seems to me Asperges would be done on Christmas this year. Definitely check with the clergy about it, and let them determine which is the principal Mass, one of the Sunday morning ones, or would Asperges be done at Midnight Mass?
Protasius, the reliable Andrew Mills in Psallite Sapienter concurs with you: "There are three Mass formularies for Christmas; each has its own proper chants. The Gloria and Credo are sung at all Masses. The Asperges rite does not take place unless Christmas Day be a Sunday, in which case it would precede the third Mass only. ..."
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