The British set up the Claims and Hirings Directorate which dealt with 'serious' looting. I would summize that there records (which I believe are at the PRO in Kew) may yield some manor of answer to your question.Does anyone know what the "official" policy of various powers was on looting?
Also (if you haven't already) a look at 'To the Victor the Spoils-(DDay to VE Day, the reality behind the heroism) by Sean Longden ISBN1844370380 could yield some information. Again this deals with the activities within 21st AGroup.
Kind Regards
Andy H