Has anyone else noticed the number of things that contradict each other form book to book?
In HBP, Dumbledore says that the ministry cannot detect underage magic. They can only detect magic. So if Harry used magic at the Weasleys, the ministry wouldn't know. In DH, all underage wizards have a tab to make sure they don't do underage magic.
There is no mention of visits to hogsmede before PoA.
I know there are many others but i don't have time to look them up.