It's vital for Russia to put the start of WW2 in 1941, because if they put it in 1939, like everybody else, then the USSR would have been just as much the aggressor as Nazi Germany, with invasions of Poland and Finland in 1939, and the Baltic states in 1940. Fortunately for them, at the time the West didn't care enough about Poland and the Baltics, and somehow cared more about the German invasion of Poland than the Russian one. But now they do care about Ukraine.