1927 Sc O214 Black 8K surcharge on 1925 7K “Decembrist” Scott 357

1927. Black 8K surcharge on 1925 7K “Decembrist”. This stamp had never been in normal postal circulation, but was sold at philatelic stores, also exist with CTO cancellations.
Catalogs: Scott 357, Standard Collection O214, Michel 337B.
Issued on: December, 1927.
Perforation: Imperforate.
Printing: Photogravure.
Surcharge: Typo.
Face value: 8 Russian kopek.