There are a few specifics with VIN exchange in Mercedes FBS4 vehicles.

VIN exchange can be executed in the vehicle via OBDII, or on bench. If the procedure would not go trough, you would need a ZN151 DS Box connection to be able to update the VIN of the unit.

When performing personalization without previously saved FBS data, you would have to set the VIN of the unit before the actual personalization, in other words, the personalization procedure stats with setting the VIN of the vehicle to the donor unit. Normally, VIN is set after the personalization. In case you use the procedure with no personalization data, it would not actually go trough, if the VIN of the donor unit is not the VIN of the vehicle.