Thanks for the info on the Spink auction. For sure I will be watching.
Your post on 01/13/2022, the 4 red agriculture revenues. 3 of the 4 stamps have a handstamp overprint showing the year 112 ( in Thai) on the bottom of the handstamp. 112 stands for Ratana Kosin Sok RS112 or 1893. The 3rd stamp does not have this overprint and it belongs to a different set used in RS111 or 1892.
The Thai dates on postage and also revenue stamps can be very confusing. Original the Thai used a calendar bases on an old Burmese system, called Chula Sakharat or abbreviated CS. CS145 is 1883. The calendar is based on the moon cycles. Deciphering the postmarks is quite complicated but if you need I have an article on that. In 1889 the calendar was changed to RatanaKosin Sok, Or RS. This calendar is based on when Rama 1 of the current Chakri dynasty moved the Capitalfrom Thonburi to Bangkok. The first year of using the RS era was RS108 or 1889. In the 1920's the RS calendar was changed to the Buddhist era or BE calendar. With BE 2500 is 1957 or the Buddhist year minus 543 is the Christian year. On postage stamps you see most of the times the Christian calendar but on other government stuff ( plus Revenue stamps) they even use today the Buddhist calendar. To make it a little more complicated, till 1940 the Thai new year started on April 1 to be changed in 1940 to January 1. So trying to decipher the various calendars into the Christian Era before 1940 is tricky. You also have to know the month. Eg ; jan - March 1892 = RS 111 April- December 1892 = RS 112