Typically when a saint is given a feast day, that day doesn't change. Normally the date chosen is the date of the saint's death. But St. Jane Frances de Chantal, a holy religious nun of the 17th century and friend of St. Francis de Sales, has gone through several changes to her feast day.
First of all, she died on December 13, 1641. This date could not be chosen because of St. Lucy, whose feast is on December 13 and has been on the calendar for many centuries.
Initially the Church chose August 21 as her feast day, choosing a day that was free and did not have any other major saint assigned to it.
This decision lasted until 1969, when it was moved to December 12, to be closer to the date of her death.
However, in 1999 St. John Paul II declared December 12 the feast of Our Lady of Guadalupe, obviously "bumping" St. Jane Frances de Chantal off the calendar.
The Church then looked to August, but St. Pius X was now on August 21 when the calendar was revised.
The USCCB decided to move her feast day to August 18, which was another day that was available in August.
Unfortunately, this day didn't last long either, as the Church decided to move her on the General Calendar to August 12.
So far this day has stuck!
Normally a feast day is easy to remember and stays on the same day, but for St. Jane Frances de Chantal, the Church wanted to celebrate her life, but couldn't find a good date to do it.
Interestingly, many people invoke her as the patron saint of forgotten people!
