How to find past flight routes between 1977/82 Latin America and the former Soviet Union? I hope now that I am in the correct place to post my question, as I have been kindly accompanied to the exit on travel part of stack overflow. ;)

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.
Here are a series of old Aeroflot schedules. In 1977, from Latin America, they flew two scheduled routes


Lima > Havana > Lisbon > Frankfurt > Moscow
Mexico City > Havana > Lisbon > Frankfurt > Moscow


It seems unlikely there were scheduled stops not listed, as if you're including a 1h10m refuelling stop at Lisbon you may as well list them all :-). Note that most of the international flights (perhaps all the long-distance ones?) went into Moscow; there were a few into Leningrad but all European routes.

However, it is possible that Aeroflot provided a charter-type service to collect foreign students (especially if it was some kind of large-scale state-backed scholarship scheme). In which case... the "hopping" route and then to Leningrad (via a fuelling stop somewhere) seems quite plausible, but finding documentation on it forty years later would be incredibly challenging.