The year postfix only showed up in the loading screen, not in content manager, in game or anywhere else.
So I found the culprit: It was a (most likely obsolete) line in extension\config\gui.ini that did it. It's probably left over from earlier versions of content manager when it had a different approach to adding this postfix. I probably enabled that option some (long) time ago and have just kept all the config files intact when updating content manager over the years.
Now, the option in content manager obivously has a different approach, and no option would touch this line in gui.ini, but the loading screen still reads and uses it.
Would probably have avoided this (and potentially other issues I don't know about yet), if I deleted all the extension config files once in a while... I'm mostly running default settings any way, so restoring my settings isn't much hassle.
Just don't mistake Norwegian for Danish. The two are as different as Cantonese and Mandarin.