Printed late ware armbands WILL GLOW UNDER BLACK LIGHT TEST. I have found SEVERAL, directly from WW2 veteran's stashes returned at the end of the war, that glow. Also, some Panzer Army piped shoulder boards and collar tabs glow due to the pink dye used during the period. So, Black Ligths are NOT the end all be all test, just another guide to be used in your evaluation IMO.
