I'm no expert by any means but I don't recall ever seeing a leather tab on a HJ or DJ belt buckle .......? To me, the maker's stamp on the tab is in the style for a much earlier Imperial era buckle. This would match with the BAG stamp which in my experience is for Bekleidungsamt Gardekorps (Clothing/Garment Department of the Guard Corps). Have also seen the BAG marking identified as Bekleidungsamt Gardekorps (Berlin). The BAG stamp has been observed on buckle tabs, holsters, visor and pickelhaube liners, uniform items, etc. Sometimes impressed into the the leather, other times ink stamped. Hard to say without better photos but I'm afraid this is a possibly original aluminum HJ buckle that has been embellished with an earlier leather tab; not original to the piece. My thoughts only ....