Feastdays calculates and displays several movable feast days of any given year, including Easter and the First Sunday of Advent.
It is tweaked for use particularly in the United States. If you run feastdays and enter the year 2008, the output looks something like this (except for the bolding and star by St. Joseph's day):
Movable Feasts for 2008 (United States)
|Jan 6||Epiphany (most dioceses)|
|Jan 13||Baptism of the Lord|
|Feb 6||Ash Wednesday|
|Mar 15||St. Joseph*|
|Mar 16||Palm Sunday|
|Mar 20||Holy Thursday|
|Mar 21||Good Friday|
|Mar 23||Easter Sunday|
|May 1||Ascension Thursday (most dioceses)|
|May 18||Holy Trinity|
|May 25||Corpus Christi|
|May 30||Sacred Heart|
|May 31||Immaculate Heart of Mary|
|Nov 30||Advent I|
|Dec 8||Immaculate Conception|
|Dec 28||Holy Family|
Liturgical Year A. Advent I begins Year B. Christmas is on a Thursday.
*In 2008, St. Joseph's day was celebrated on March 15, not either March 19 or March 20. See below.
There is NO guarantee that the dates given by feastdays will be accurate. The dates given by feastdays are 'accurate' in the sense that they accurately follow the c. 2000 AD rules for determining feasts laid down by the bishops of the United States.
However, for bishops, who can make a Thursday into a Sunday (such as the Ascension, although in some U.S. dioceses, it's still Thursday) -- who can make any day of the week you want into a Sunday (such as the Epiphany) -- anything is possible.
For example: in 2008, March 19 (St. Joseph's day) falls during Holy Week. There was no current rule for this possibility. That 2008 would eventually happen apparently never occurred to anyone.
On the other hand, the 1960 Codex Rubricarum, perhaps more forward-looking than modern liturgists, did have such a rule: "proximum sequentem diem"; literally, "the next following day," which means the next day after March 19 that you could legally do it.
Sundays are out. Holy Week and Easter Week are obviously out. Also out, as it happens, is the Monday after the second Sunday of Easter (the day after Easter Week ends), which (by already established rule) in 2008 is given to the Solemnity of the Annunciation, because March 25 occurs during Easter Week.
So, even though no rule was currently in place, the logical place for St. Joseph's day in 2008, and the place it would have had under the old rubric, is "the next following day" after Monday, March 31; that is, Tuesday, April 1.
So what happened? In 2008, St. Joseph's day was celebrated on March 15.
A mere computer program can not cope with miraculous events. You should not expect it to.