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How are all the Russian and USSR stamps listed in Scott catalogue. for instance the old USSR countries that are still issuing stamps after USSR broke up?
I think you're overcomplicating things. Looking for stamps issued by the USSR? Look under USSR. Want stamps issued by Lithuania? Look up Lithuania, you'll see issues from 1918-1940 and from 1990 to present. Uzbekistan? Go to U in the catalog.
There's no reason for it to be any other way. Recognized, independent, sovereign nations gets their own listings.