Great answer from Fr David. However how do you find the liturgical readings for any specific day in HX? Is there a formula to use? Or a calendar to refer to? How did Fr David know this answer so quick?
The last part is easy: the OP was asking about the feast of the Assumption. That made it very easy to lookup. It makes no difference what year it is (either calendar year or ABC), or what day of the week it might happen to be, the readings are always the same. Also, I happened to have an old Lectionary handy (one in use at that time). I checked it against the readings in an 09 missallette just to see if they had not changed (unlikely that they would have changed in any case).
As to the first part, that would depend on just how far back in history one is going. Since this question dealt with the time of the novus ordo Mass, it was very simple. Ask about 1648 and it might take a while!
My 1974 Sacramentary has a table in the front listing the calendar from 1974 to 1999. It would be an easy thing to simply look at a date and determine where it would be in relation to one of the major feasts listed.
For example the year in the OP is 1981:
Year A weekday cycle I (odd number year)
Ash Wed. 4 March; Easter 19 April; Ascension 28 May; Pentecost 7 June; Corpus Christi 18 June; 8 weeks of Ordinal time ending 3 March and resuming on 8 June for 10 weeks. First Sun of Advent 29 Nov.
There does seem to be some kind of misprint in the last column, because every year it only lists between 6 and 10 weeks of Ordinal Time after Pentecost (which can’t possibly be accurate unless there’s a column missing). Curiously, the Lectionary has the exact same information
But other than that, it could be a handy little chart to lookup when a feast was in the past.
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