"Best Before Date" (BBD) is a mandatory info to indicate in the file. 

"Used by Date" (UBD) may be mandatory or not, depends on the case. 

In case UBD is not mandatory, you can add "raw" in XML and indicate BBD only (which is okay from system side). 

IMPORTANT: If both are set UBD and BBD, the UBD overrules the BBD (but this a display thing, the data of both is in the system)