I think he is more in the know than you think. He was right that we were in talks with Mattock and Trotter but because neither of them signed everyone started doubting him. If he says Vicente has signed, I reckon Vicente has signed.No he didn't.
He started a thread saying "someone is here at the amex, if he signs it will be great". No names from sitch. Other posters guessed it was CMS, because at this point everyone knew we were in for him, any way.
His accuracy was covered in the original mattock to sign +trotter thread. Mattock to sign and another player in talks - Page 15
It's seems pretty likely that sitch does work at the amex, and might hear things, but is rarely the first to hear them, and often is saying things we already know. I don't know if this is one of those cases where his working at the amex gives him confirmation, or if the people working there are just passing on the same info we already have (gus saying it was 90-95% done and Kaz tweeting it was done).