For instance, I was recently contacted and asked if I knew when the set C - 19 was issued. I looked at 6 different PRC catalogues and see three different dates: 1952, Nov. 15 in three, 1952, Oct. 25 in two, and 1951, Dec. 14 in one. The xa.business.com site does not show an issue date.
My earliest CDS for a postally used stamp of this set has a Tientsin, 1952.12.1? cancel. I have another dated 1953.2.11 with the top of the cancel cut off, so no city PO indication.
Anyone have a magic crystal ball out there they can ask?