Once or twice is coincidence. Happening for numerous people, with predictions about what will happen 10+ years later, correct to the year, without a single error, does not sound like coincidence to me.
How in the world does cold reading predict what will happen 10 years down the line? Cold reading can judge what has happened to you or try and guess something about the past; not about what will happen. If it was generic and said that it will happen 'at some point', then yes, it's probably a guess. Stating the year however does kind of change things.
Obviously your grandfather was something special. I'm sure he'd have a chance at the James Randi challenge. If he's still knocking about there's a million quid to win. Get him signed up.

