ANSWER: I know the way we talk about Holy Days can often be confusing. However, there are set Holy Days of Obligation that do not change from country to country or diocese to diocese, but are universal. They are:
1. Every Sunday
2. January 1, the solemnity of Mary, Mother of God
3. Ascension Thursday (Thursday of the Sixth Week of Easter)
4. August 15, the solemnity of the Assumption of the Blessed Virgin Mary
5. November 1, the solemnity of All Saints
6. December 8, the solemnity of the Immaculate Conception
7. December 25, the solemnity of the Nativity of Our Lord Jesus Christ.
Additionally, the bishops of the United States have decreed that when January 1, August 15 or November 1 falls on a Saturday or Monday, the requirement to attend Mass is suspended. Also, in some dioceses, they have transferred some of these celebrations to the nearest Sunday, for example, in some dioceses Ascension is celebrated on the Sunday after Ascension Thursday. In any case, they haven’t eliminated to Holy Day, but transferred its obligation to a different day.
As for the Sacred Triduum (Holy Thursday, Good Friday, Easter Vigil); I have never heard of Holy Thursday or Good Friday being referred to as a Holy Day of Obligation. Only Easter Sunday is.
My personal opinion is that we should keep holy days as they are. They are holy for a reason - because of what they celebrate. I personally don't understand how a holy day reduces its rank simply because it falls on a Saturday or a Monday. It IS a holy day and we should celebrate it as such. This business of transferring or abrogating the obligation is silly and just confuses people.