Hello Rob
so it could have been - I know from files of Augsburg about 20 years before that the French in Strasbourg did not accept those underpaid letters and told Augsburg internally to give them the correct amount of money they owe to them and Augsburg had to pay (in some few cases about one Gulden, what was a lot of money in the early 1850s).
But the French postadministration was very good, much better than the Bavarian one, and mistakes from their postofficers are very, very rare and so I am very happy to show one of those few I´ve ever seen.