Note: This post originally appeared on the blog of my since-shuttered analytics firm: Axiomatic. That said, if you need some analytics work, get in touch
A long time ago, I had published advice for event organizers to save a few characters and leave off a year reference when picking a Twitter hashtag for their event.
The thought process at the time was that you could only search seven days worth of tweets and the year addendum was kind of worthless in that environment.
Now that Twitter is indexing and making searchable their entire corpus of tweets, that recommendation needs a change.
If you are in charge of picking the hashtag for an event or some other time-based thing, you should probably strongly consider adding a year or date indicator to the end to make later searches a bit easier.
It would appear you can time-limit searches, but that sort of advanced maneuver isn't something you can expect all users (or all embedding platforms) to grok.
So, the new recommendation:
When in doubt, include the year. It'll make your event tweets easier to find later.
Oh, and as always, make sure you let participants know what the official hashtag is so you don't end up with multiple streams like the #rubyconf examples above.