There is no secret or magic as to how Al gets his info. Al spends all of his time on this. You could do it too, if you spent all of your time at the parks, interviewing guests, cast-members, suits, analyzing pictures, etc, etc.
Sometimes he reports what is released from Disney themselves. Other times, he reports things that may be rumors, but have enough legs to them that he thinks they are newsworthy. He also reports things drawn from conclusions he makes by observation.
Al isn't infallable. He makes mistakes. Sometimes, his impressions are wrong. Other times, Disney changes their plans. But he does dedicate himself to reporting as much as he can. Like him or hate him, he does get an awful lot right.
And when he does, he is first to take credit for it!!