My apologies. I checked and there were plenty of Poles (at least 50 percent) living in the “Kresy” (eastern part of old Poland annexed by the USSR) pre-1939. The rest were the ethnic minorities I mentioned, along with a bunch of others. Lwow was 2/3 Polish!
OK. I also checked to find out that the far eastern regions of pre-war Poland were indeed dominated by the Ukrainians, while the territories close to the present day Poland were almost entirely Polish (and Jewish.) Hence, the bitterness among today’s Poles with regard to the loss of Lvov.