2 month anniversary.
First kiss. First sexual experience.
First time holidaying together.
6 months anniversary.
One year anniversary of the third date which they declare that they love each other and then consented to have sex and then move in together before deciding not then did it anyway.
You get the idea. Couple who are so into each other will try to find all the excude in the world to have an anniversary for anything. Let us spell that.
Until they get married.
For me, all bets are off.
When you get married, there are only 3 events which need to be celebrated.
The day you get married (or solemnise your marriage)
Either spouse's birthday.
That makes it three.
That is, until you get children...
Just another celebration