A last chapter in WWII era Tuvan philately...there weren't large stocks of any stamps left to surcharge but at some time (presumably at the same time that the Kyzyl surcharges were applied to the high valued stamps), other quantities of low valued stamps were also revalued to 20-30k postal values.  These were revalued with indelible pencil by hand.  This is probably the most dangerous part of Tuvan philately...literally only a couple of each example survive and expertising them is almost impossible.  Their existence is not a question (Blekhman got information from the horses' mouth, plus there's the interesting Negus story).

So what's the Negus story?  Well in 1958 he was trying to get a modern cover with cancel from each of the 21 post offices that were in the Tuva of the time.  He wrote to the postmasters in Tuva with a SASE to get the cancel.  Six of the postmasters sent back the cover, and in one a local Tuvan had enclosed a bunch of stamps he had accumulated and thought Negus might enjoy as a stamp collector.  A couple of the enclosed stamps were common Hungarian stamps that the native had encountered, but there were also used copies of the 1942 and 1943 issues...and a couple of them were these (at that time unknown) revalued stamps!

A couple of other oddities are worth noting.  There were two additional essays made for the 1942 issue.  They were for 25K and 50K.  The 50K value was supposedly put into postal use, but no copy of the stamp has been found yet. 

Also, when the soviets assimilated Tuva after the war, the remaining postal stock of the 1943 issues were collected and sold out.  Later, (in 1946) the designer of the stamps (V. Demin) reprinted some of the stamps for collectors, but they lacked the framelines of the postal issues and were in a different color.