2012. Look at the date of the post.
Go look at my post above - you simply unsubscribe from whatever calendar that’s been selected (assuming it even has one, which most complainants don’t) and subscribe to the correct one.
Whatever year you wish to go with the overall question remains - why the change?
Also, as a user on the official Apple forum has noted today:
“I shouldn’t have to manually add Easter or Good Friday into the calendar on my phone”
Bad PR all around.