Some years ago I purchased a small BOB lot, mainly because it had a bunch of US Officials.
The lot also included a number of Postage Dues, including an imprint plate number strip of three J31, pen cancelled, but full original gum, never hinged.
Also included were 5 x 5 blocks of all denominations of the 1931 postage dues. These are no gum, all cancelled "Kansas City MO (129)", and appear to not be postally used either.
Thanks to a page on Riverside Stamps' website, I learned about "receipt use" of postage due stamps, although this explanation doesn't made complete sense to me. Is this explanation correct for how apparently cancelled but postally unused stamps were issued?
And the J31's. Are they considered "used", since cancelled, or mognh, because they weren't postally used and are ognh? Or something else not listed by Scott's Specialized?