Better convince me quick.

How should I know what number you reported to the table? I was busy watching the players and getting them ready for the next play. If I learn that you reported an erroneous number after a couple of trips up and down the floor, I'm still going to come discuss it with you and expect you to fix it.

That's the difference with this situation and giving help on an OOB call. With the OOB call your partners can clearly see which direction you are indicating and the discussion can happen right away, but with foul reporting your partners generally do not watch you and probably won't know until later that a mistake was made.