One never should make assumptions in any game... and Rune Factory Frontier is no exception. Although once any new Festival appears on your Calendar, it will become a permanent fixture, the Formal Dates that are designated for each season do not remain on the Calendar.
Any Formal Date will appear on your Calendar with a Star and a description only after you ask a Girl on a Date during THAT season and she accepts the invitation. Once the season ends, the Date no longer will be marked with a Star.
It was only when I was trying to pinpoint the actual moment that the Date would be added to the Calendar that I thought to look at the Dates for previous seasons. Although I had taken an Eligible Girl on a Date each season, no Star marked those Formal Dates after the season was past.
The Formal Date Star and description therefore is a temporary Calendar addition.
The reason I am posting this is because a player asked me how she could add the Night of Holies to her Calendar. I told her that she needed to ask an Eligible Girl for a Date during Winter before it would be marked on the Calendar, which was correct. What I did not realise then, however, because I had not paid sufficient attention to my own Calendar was that, once the season is past, the Star disappears...
The Night of Holies may be an exception to the general rule as it corresponds to the Starry Night Festival in other Harvest Moon games. As I am in the Winter season at present, however, I shall have to wait until next Spring to see if it remains on the Calendar afterward or not.