It's just the convention to put the year in the title when the article is older than a year or so.

Historical material is always welcome on HN and it's fun for readers to know what year an article dates from.

Nah, this is the bible of NAT traversal: https://bford.info/topics/Network-Address-Translation/ (2005)

This old post too:

https://www.zerotier.com/blog/the-state-of-nat-traversal/

There are lots of others. The TS post is well written though, and contains some interesting information like the way the birthday paradox relates to punching symmetric NATS.

Man I wish there was more documentation like this out there, too.