Luca Turin claims that Eau de Joy was the same as Joy EDT (or edp?), but I have never smelled an eau de joy. I do not think there is currently any eau de joy in production. Vintage Joy parfum is more vivid and richer than the edt - more of everything, deeper, and more long lasting.
I have not smelled the most recent (post 2010) reformulation. LT claims the parfum is now very rosy (jasmine having been severely restricted). I actually stopped by the Patou store last week and they didnt have any Joy parfum, they said theyre waiting for the new batch, which wont be ready until spring 2013.