Houfton – I’ve looked into this and I think I’ve found the cause. If you’re using a ?year=2015 GET parameter you will get a 404 page if you have no posts created in 2015. Weird, huh?
If you’ve made a post this year (2015) you will find that the problem you had in 2014 is now gone and you can use the ?year=2015 parameter now, as well as ?year=2014.
Best use something else as you said, like “annum”.
I suspect that this is because of the year archive page. Try this yourself on your blog. Go to https://www.yourblog.com?year=2015 – it redirects to https://www.yourblog.com/2015/
I’m not in the habit of resurrecting old posts, but I thought this might help out someone else with the same issue.
