Premise: San Marco 1, also known as San Marco A, was the first Italian satellite, and the first non-Soviet/US spacecraft. Built in-house by the Italian Space Research Commission (Italian: "Commissione per le Ricerche Spaziali" , CRS) on behalf of the National Research Council, it was the first of five as part of the Italian-US San Marco programme.
Hypothesis: The Italian-US San Marco programme continued its work after the fifth satellite was built.