Interesting. I used to have the Journal of Chinese Philately article referenced in Stamp Forgeries and it was very helpful. Sold it in the lot when I sold off my original collection. I have a copy of the stamp above. It looks sharper than the scanned one above but I'm not sure now if it's fake. I will see if I can get a scan up. I bought it from a dealer in China so who knows? I didn't overpay for it so I wouldn't be crushed if it's a forgery.
Heinrich Koehler Auctions just listed a huge Mongolia lot on SAN. No photos, would love to see the stamps and certificates. Here's the English translation:
1924/2021, very extensive mainly mint never hinged, initially also a little unused collection, in the main numbers almost complete with many special features, neatly collected in seven Palo albums (with slipcase), a total of over 1000 issues with over 4,000 stamps, approx. 450 souvenir sheets and numerous miniature sheets. Only two single stamps 20 and 40M from 1954 and the temporary fixtures not listed in the Michel catalog (1941) are missing. All regular early issues are available, including the 1926 POSTAGE "hand stamp overprints in purple and black, the very rare issues from 1943 (with 60 mung), 1951 (30th anniversary of the revolution), 1953 (Tschoibalsan), the blocks 1- 6, all early cut blocks, overprints and overprints, airmail issues, Olympia block (1976), 12 silk blocks for the football World Cup (1982) with and without overprint, gold and silver stamps (1993, 1997 and 1999), foil sheets, all Genghis Khan / Secret history of the Mongols editions (1962-2020), animal calendar, countless editions on fauna and flora of Mongolia etc., in addition to an extensive collection of large and semi-circular sheets (28) 1970-2020, as well as EXPO'70, art and customs, animal calendar, indigenous fauna and flora, Mongolian saiga, Przewalski's horse, Genghis Khan, human history, sacred mountains, calligraphy, historical saddles, ancient means of transport, anniversaries of the end of WW-2, Olympics Atlanta. 1996, national costumes and others as well as miniature sheets (136), good condition, some early issues competently signed or with findings / certificate with photograph