Ah - found it -
var d = new Date();
On another post. Change PC date to next year and it updates the year of the date viewed.
I note that you seem to have found your solution and that's cool.
For starters, I edited the footer area of a Master Page. In that footer I clicked Insert > Fields and Variables... This presented the Fields and Variables dialog.
From there I clicked New and replaced the default in the Current format field with yyyy.
Helpful and Handy Links
I tried that ... but when I moved the PC date into next year and refreshed the browser, it didn't change the date. It seems to insert the build date.
That's why I used the script - works every time.