This is something I don't really agree with HN policy on. If things are still applicable I think it doesn't matter if they are from this week or last year and stories are interesting precisely because they are timeless, not timely.
I am planning putting the original pub dates on stories if I can manage to grab it from metadata, but as this site doesn't include dupes I'd like to keep dates out of titles. I'd also like to surface old content to the home page though when a few people vote for it around the same time, need to look at ways of doing that.