No matter what they say, "Invisible" was supposed to be the first single from SOI. They had a massive rollout for it which included a Super Bowl commercial, a tie in promotion with RED AIDS charity, Jimmy Fallon performance, etc. SOI was supposed to be released in April or May of 2014, and the tour was to begin in September 2014. No matter what revisionist things you've heard, that was originally the plan. They could've back out of "Invisible" due to the Super Bowl/Charity tie in, so they had to go through with it. SOI came 8 months after the first "single".
Let's wait until next Wednesday, it sounds like we're still definitely getting "Best Thing". Maybe they'll at least give us a release date.
They never once said invisible was of SOI though, they have with the blackout and now TBT which they are saying is "the lead single from upcoming album songs of experience" they go any other way other than release this album then they will be a complete laughing stock, they have put it all out there