How to find past flight routes between 1977/82 Latin America and the former Soviet Union? [closed]

I hope, I am in the correct place to post my question:

Is there a way to find past flight routes between Panama City and St. Petersburg (former Leningrad) in the years 1977 to 1982?

To be precise: over which flight route would someone reach to either from Panama City to St. Petersburg and vice versa in the late 1970s?

I would need this information for an historic background check up in my genealogical (family tree) research.

Bonus point: I have heard that especially in Latin America, flights back then would "collect" passengers (part of student exchange programs between Latin America and the former Soviet Union) from capital to capital before the plane would go into the intercontinental flight, e. g. start in Panama City, going to San José, Costa Rica, to Managua, Nicaragua, to Belize City, Belize to ... to Havanna, Cuba. However, I am not sure about this claim.