The first slide shows one of the boxcars from the train that left Paris on 15 August 1944. The map on the second slide indicates that the prisoners took 3 different routes to get from the blown out bridge to the train at Gare de Nanteuil-Saacy. The group of prisoners who loaded wagons and carried the belongings of the military and civilian passengers and dignitaries to the town followed the red line and returned. The mass of prisoners, the airmen included, then marched along path indicated by the black line. This map indicates that some subset of the prisoners stream took a longer route to get to the train, but I have been unable to find out who these prisoners were and why they were diverted. The memorial society has disbanded and the people involved at the time it ceased operating did not know any of the details.
Similar transport trains had already carried roughly 1.8 million French citizens to slave labor camps in Germany. Excluding the airmen, there were 2284 prisoners on the train leaving Paris. Of that number 458 men and 370 women made it back home after the war ended.