Right, except that both can be fulfilled by the same Mass. See Canon 1248 §1. A person who assists at any Mass on the evening of the first of two consecutive feast days has assisted at a Mass on that feast day, and assisted at a Mass on the evening before the second of the feast days. Simple as that. Naturally you have no documentation, since the Church has never seen fit to increase peopleâs obligations in the way you propose.
Really, I think your mistake originates in the very idea of thinking about âtwo obligations.â A person no more has âtwo obligationsâ in such a case than she would have âfour obligationsâ in the average month. Rather, she has one obligation, Canon 1247: âOn Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass.â It does not say âin one Mass apiece.â This is why when Sunday and another day of obligation coincide the obligation requires assistance at only a single Mass, not at two. âObligationsâ are not additive â three obligations, twenty obligations. If they were, then the obligation to attend on Sunday and the obligation to attend on, letâs say, Christmas (when it falls on a Sunday) would each equal one Mass, and so the total would add up to two Masses. âNo twofers!,â one following your reasoning would exclaim. But as we all know, thatâs not how it works â and this is not because we make one Mass âcount for twoâ or because âone of the two obligationsâ is waived or suspended that year, but because there only is one obligation â Canon 1247 â that is relevant in the first place.