I recently noticed a mistake in Zoo Day, it isn't a big one, but shouldn't Maggie's primary language have been Spanish? We see her thoughts, they are in English, and she never appears to experience language barrier, confusion, or to search for words. She may even still have a Hispanic accent.
I mean, it is reasonable that she may have learned some English wherever she was, but it certainly wasn't the primary language she used. She would only have had to start using English when she moved in with the Carpenters. There has been no discussion of language/culture issues, which is easily explained in most books by Harry being totally unaware of them, even if they existed. But in this book we have her viewpoint, and there doesn't appear to be any acculturation issues.
Just a thought.