With the servers gone, developer communication and the client data are the only verifiable primary sources on the game left. It'd be loony not to accept both.
On to the details, then?
The development and release history of a feature, including when and whether it was discovered or announced, and when and whether it went to beta or live, is something I expect in articles on a game wiki. Besides, if the wiki just says "Wind Control was a set" like "Earth Control was a set," readers might get the wrong idea about what was actually happening in the game.
Also, for verification's sake, features that were discovered but not announced should specify, somewhere, how the features were found. Not as a mark of shame on the article, but just so people know we didn't make Wind Control up.