All of those were held in the same year many times. And San Marino is like 100KM away from Imola.Two different tracks in the same country but not held in the same year,or as for San Marino is a small principality I believe so thats why Monza is the Italian GP and San Merino is (was) the San Marino GP, I think that was what it was about when I heard or read it somewhere, someone wanted to know why Italy had 2 GPs a year. Probably more to do with WORLD CHAMPIONSHIP status , sounds better with a county name in the title, they cant call both races USA GP. Like when they were thinking of dropping Hockenhime for another German track why not both. Or the year they dropped Silverstone for Donington in 93, but at the end of the day they can have them anywhere were people want them. I'm sure they don't think of themselves as a charity fun run. Follow the money.
I must say I never was a big fan of the whole "these countries have no racing history behind them" line of thinking. No country had a GP history until people started hosting GPs there .Just becuase Vietnam only now has the money to organize such events doesn't mean they should never have the oppertunity.At the end of the day, the only rule they're going to have is to send the races where the money is. You can already see this in action right now, with races in (and scheduled for) countries that have no real racing history behind them