In Deauville, the newspaper headline announcing the outbreak of the war incorrectly states, "Archduke Francis Joseph" had been assassinated in Sarajevo. Francis (Franz) Joseph was the reigning Austrian emperor and was most certainly not assassinated. His nephew and heir to the empire, Francis (Franz) Ferdinand was assassinated.
Old Coco is wearing triple pierced earrings. She died in 1971 and multiple earlobe piercing didn't become fashionable until the 1980s.
When Boy and Coco are talking in the snow scene the snow does not melt when it lands in their hair or on their clothing. It would have to be extremely cold for that to happen. Also, the "snow" clumps in bubble like mounds. Real snow doesn't do that.