Well said Pedro!!
They didn't actually use John's research. Who Do You Think You Are? just ended up finding out the same information as John. They didn't steal John's work. The people working on the show weren't to know that Damien had already gotten John to do this research. How were they to know if Damien didn't inform them? I'm not putting any blame on the research team anyway. It was only Damien who was being a bit dishonest about it but I can understand why he did it since it allows for an interesting story to be aired about his family.
That explanation was added after the original post.
I assume that the explanation that you're referring to is his reply to your post on the blog. However, he hasn't changed his original blog post (at least not since I read it before seeing the Boards post and I'm sure he would have added it as an edit at the end). He made it clear in the article that they didn't steal his work without the need for an explanation from the following:
I read the blog post on 17 Sept and posted here. I believe it was clarified afterwards and, with due respect, that is what you read.
I didn't enjoy either first or second programme. Regarding Damien Dempsy's one, I never felt he showed much interest in what he was being told. Little did I know that he already knew it. Pat Shortt's programme was a disappointment, I had too many questions at the end of it. In the trailer Bertie Aherne said he hoped they don't find any Royals. I wait with bated breath! On a more positive note, I loved John Grenham's blog post about Damien!