I have the same problem every time January comes around. I have the year in the footer after the copyright symbol. I change the year by going to Master View, searching for last year (2014) and replacing all with this year (2015). Must go into all PowerPoints to do this. Sigh.

I also see that when I'm in master view with the Insert menu showing, I can click on Header and Footer, and choose Include on slide - Date and time. And it will update automatically! Woohoo! Except it won't give me the option of including just the year. Stupid PowerPoint.