Chet has it right. Unless the miscounted amount of player's chips is a substantial amount more than is stated (10% is a good measurement), we can reasonably determine that the action should stand.
If the dealer says, "All-in for 47,500" and it turns out to be 72,500 because a 25K chip was not counted until after the river card is dealt, I would only hold the player calling the bet liable for 47,500. 25K is a substantial amount more than what was stated.
On the other hand, if the player calling the all-in has a large stack, 250K for example, and shows down two kings, a reasonable man may easily decide that the overlooked 25K chip did not affect the action. The winning kings should get the full 72,500.
This decision is about fair and reasonable evaluation of the circumstances.