The agreement for the crew to film in Saint-Antonin-Noble-Val, France was that they must allow the local residents to be filmed as extras. Because of this, most of the citizens seen in the Saint-Antonin-Noble-Val shots are real citizens of the town.
The schoolteacher played by Anton Lesser was called "Benech" in the novel, but the small French town in which much of the movie was based had a popular mayor whose name was similar, so officials asked that the name be changed. He's called "Renech" in the final version.
In the opening shot of the train crossing the viaduct, the coaches are BR Mk1 ones, which were not built until the 1950's yet the interior shots of the train show LNER on the antimacassar, which would be correct.
There are several train scenes but in most (not all) of them the sound effects, mainly the whistle, are those of North American trains. European steam engines had a very different sound. Even the sound of the tracks is different in Europe because of a different type of roadbed.
In some shots of the departing deportation train, it can clearly be seen that the goods wagons used bear the inscription "UIC St" and a rather long wagon number. Both things belong to the international UIC numbering system, not introduced before 1965.
Charlotte Gray: [narration]
It all seemed so simple. We were at war. The Nazis were the enemy. And because good must triumph over evil, so we would triumph over them. How could we have know that war ever trades in such certainty? That we are nothing is unthinkable. Anything could be true. Even a lie.