When they visit the Berlin Jewish cemetery at the end, there is a headstone for someone who was murdered in a concentration camp. But there are no such headstones, as concentration camp victims' bodies were burned and disposed of in the camps, they weren't brought back to cemeteries for burial.
I must disagree. There are numerous headstones in Jewish cemeteries in Germany that list the names and dates of people having died in concentration camps. Thus a stone like the one depicted in the film, may well have existed.