You also have the problem of selective enforcement. I spent a week one time travelling to different recovery sites in France with military, MFA and MOD officials, listening to them explain the different laws prohibiting the collecting/sale of military ordnance. Then as we would stop for fuel you would see fuzes, etc. for sale in the gas station windows. The same in different parts of Belgium. A lot of the confusion comes from what is the actual law and what is the common practice. Once an accident occurs or it is brought to the public's attention, enforcement is tightened up, then it becomes difficult for eveyone.
Part of the problem with shipment to the US is that it has been generally illegal for decades in the US to import most military equipment. Doesn't matter is it is US manufactured, WWI, etc. There are forms you can fill out and try to run through ATF and/or Customs, but lacking these if it is caught you will generally lose it. A lot still gets through of course, but about 6-7 years ago the US started putting pressure on European countries to tighten up on mail sent to the US. I had packages which I sent from my hom in the NL to home in the US refused and returned by the NL. I was licensed to own the items in the NL, but they would not let me ship them to the US. Anyone selling to collectors in the US has to take into account what happens if the package is lost, seized or returned. Not good business.