2 points...
1) Not going "official" might just give Disney the ability to float start dates. Maybe if they are not ready for a particular refurb, etc, they could bump it off a week, or more and some people get a little extra enjoyment.
2) Lets define OFFICIAL... when Disney releases a press release, posts on the blog, tweets, or makes some sort of open announcement that something is changing then its "Official"
everything else is varying levels of confidence in a rumor. You as an individual must decide for yourself what level of confidence in the rumor a particular piece of info gives you. Sure the CMs have been notified about something, ok, thats a fact, but it doesn't make the closing official, is simply makes the rumor more than likely true. On the other hand the "rumor" of Soarin going down for 6 months early next year isn't as confident of a rumor, even with the "CMs are being cross trained for the closure" note added, I still think its an iffy rumor. Now, when you can't get FPs for it, then the rumor becomes more credible.
When does JTA become "Official" most likely October 5th, when it has been closed a day and signage goes away, or some other physically tangible thing happens.