Ok, so family game night and my older son joins us. He can get VERY competitive when playing games.
He watches everyone's cards and the SECOND their 2nd to last card TOUCHES the pile he screams UNO. My wife tells him that he can't call UNO on her until the card is out of her hand. So a couple hands later my daughter calls UNO as she moving the card from her hand to the deck and he starts yelling that if he can't say if until the card is out of her hand then she can't say it either.
All I see the official rules is that if a player calls attention before the next player goes, and I've always gone by "chess rules" where once the card leaves the hand entirely, then it's fair game to be called out.
What's the official ruling on when exactly they player can be called out for not saying UNO?