Patzer

The six priests returning by train from Lourdes assemble behind an exit on the right side of the train as it pulls into the San Martin station, but when the scene switches to an exterior shot of the train platform, the priests descend to the platform through a door on the left side of the train.

In the first 5 minutes of the movie it is supposed to be 1939 and the Loyalist (Republican) soldiers are crossing into exile on the French border. As they cross over they are turning in their guns and the first one to turn in his gun turns in a Soviet PPSh-41 sub-machine gun. The PPSh-41 was not developed until 1941.

Towards the end of the film, when Gregory Peck is digging up the guns, he unwraps a Sten gun. The Spanish Civil War took place from 1936 to 1939 and the sten gun wasn't in service until 1941. This means that it couldn't have been buried when they fled Spain.

Paco is obviously Italian, not Spanish.