Intrastat - Mode of Transport missing in purchase order header

We have a problem where for a supplier there is missing import data for some materials - but not others. As far as I can tell the Info Records for those with missing data are identical to those where there is no data. For example, the Incoterms field and the Mode of Transport fields are blank. The Country of Origin field on the Info Record for both of these materials is DE. Does anyone have any ideas about what may be causing this?