I wonder if George's life really is too controversial? I mean, it's been discussed in other books and, obviously, documentaries. The royal family has even in recent years discussed Nazi connections in Philip's family in Royals and the Reich. The lives of the Mountbattens were certainly more scandalous (sexually) than George's. Drug use really isn't that shocking anymore. I don't see why they would block research into it unless first-hand material was destroyed at the time--when it would've been a much greater scandal.