They were labeled 20th century, there's no reason to suspect they would have spent any meaningful amount of time in the elements, nor is there even much reason to suspect that they're fake when authentic would have been likely been cheaper anyway. Anyone trying to make a fake would like put more labor and effort into the production of such items than the natives would and the value of their labor is likely higher to begin with. Meanwhile a colonial trader could just set up a contract to receive a number of native cultural artifacts in exchange for some cheap booze or whatever.
They were labeled 20th century, there's no reason to suspect they would have spent any meaningful amount of time in the elements, nor is there even much reason to suspect that they're fake when authentic would have been likely been cheaper anyway. Anyone trying to make a fake would like put more labor and effort into the production of such items than the natives would and the value of their labor is likely higher to begin with. Meanwhile a colonial trader could just set up a contract to receive a number of native cultural artifacts in exchange for some cheap booze or whatever.