Mind that for such sources the copyright is no longer in effect (books published in the USSR before 1971 are no longer copyright-defended if the server is in the US).
Whose law are you getting this from? Russia has recently adopted the life + 70 rule, and though there is some confusion about how the transition from life + 50 would function none of that would support your speculation about the law.
Yes, but the law is not retrospective. So if work already was in public domain then it's remain in public domain. (example until 1963 in USSR photo works was protected only 3 year). I think we need [[Copyright in Soviet Union]] article. At present I can refer to acts/articles/legal authorities only in Russian language (example http://ru.wikipedia.org/wiki/Project_talk:%D0%98%D1%81%D1%82%D0%BE%D1%87%D0%...)