I'll have to check on that, but one of the key things is that Harry Potter is huge in the States, whereas dad has taken a while to really get going there and it's only in the last couple of years with books like Maurice and Wee Free Men that things have started to pick up.
As an aside, I ended up having to pick up an award on behalf of my dad last night for ‘Best Author’ at the SFX (UK SF/Fantasy magazine) awards. The event was so badly organised they had 1) Not invited my dad 2) Not told him he’d won 3) Not told ‘me’ he’d won and therefore that I’d have to go up. I just happened to be there because I do a bit of work for the mag. Madness.