The 15cMG1-SO with Wavy Rays watermark, although uncommon, is not nearly as rare as the regular issue. The stamp was used in the early 1950s and continues to puzzle me. It has a watermark consistent with the 1E3 or 1L1 grids. I am still not sure which of the two is correct. For now, I will classify it as a 1L based on the years it was in use. These two specimens show weak and strong overprints.
These two papers look slightly different. This post is a place holder for future work.