What is the ruling on swearing on the Qur'an with sincere intention, then remembering an incorrect detail that was unintentionally stated after the oath?

There is no sin upon you, nor expiation, if you swore an oath believing yourself to be truthful, even if the matter later turns out to be otherwise. This falls under the category of a "laghw al-yameen" (a a vain or unintentional oath), as mentioned by Al-Qurtubi, Malik, Ibn Abbas, and others.