I have one of the 10s that has no overprint as shown in this info that I got online. The photo of the exact stamp of mine is also attached. First the info and then the photos
An interesting story lies behind these.
Stamp 2: Arbe (Rab in Serbo-Croat) is an island off the coast of Croatia, and now part of that country, but after the First World War the Italian-speaking residents wanted the island to become part of Italy. Instead it became part of Yugoslavia until during WW2 when the Italians installed a concentration camp thereon.
Stamp 3: San Marino Fascists were going to celebrate 20 years of fascism, but the series of stamps was never issued due to the fall of Mussolini
Stamp 1: The fall of the fascists on 28th July 1943 was commemorated using the overprint.
Stamp 4: The creation of a provisional post-fascist government was commemorated using a different overprint.