If I'm fairly sure I or someone else saw any part of another player's pitched card, I'll say, "That flashed." But dealers, being in a hurry, then ask me to identify the card, and I
WILL NOT PLAY THAT GAME (the one where I say I saw it's the 7
and they tell me it's wrong because it was the 9
). If they don't want to believe me, then the person can play on with me knowing something about one of their hole cards.
Obviously it's not hard to construct a situation where knowing "odd numbered black card between 5 and 9" is a huge advantage. Conversely, it's impossible to construct a situation where I can get a replacement for my opponent's ace that wasn't exposed (unless I'm just picking cards by dumb luck and happen to get an ace). Therefore, dealers and staff should always err on the side of believing the player who saw the card unless there's clear time-wasting going on.
Nowadays, though, I mostly just keep mum until I know I'm going to play the hand, because it's one of those cases where I've learned that speaking up just wastes even more time as the floor asks you to identify the card. Of course once I know that, it's too late to speak up about a pitched card, so I don't worry about it unless I'm pretty sure the precise rank and/or suit.