What is the ruling on eating chocolate that was later discovered to contain alcohol, given prior knowledge that only one type contains alcohol, and the eater was unaware of this until after finishing eating?

There is no blame upon you, because you ate trusting the man's word, and believing that the food was free of alcohol. Allah has overlooked mistakes and forgetfulness, for He says: "Our Lord, do not impose blame upon us if we have forgotten or erred," and the Prophet (peace be upon him) said: "My nation has been forgiven for mistakes, forgetfulness, and what they are forced to do."