I really don't know what you mean with the first question, but the answer to the second question is a definite yes. The Potsdam conference of 1945, between the UK, the USA, and the USSR, officially shifted the borders of Poland significantly west.

At the Yalta conference, the Western allies essentially agreed that the eastern border of Poland should be based on the Curzon line, a line significantly west of the interwar border of Poland. This line (which is essentially Poland's current eastern border, with a few changes that occurred in the fifties) was proposed by a British diplomat during 1919 but hadn't been implemented then. So the USSR got the easternmost chunk of interwar Poland, including the cities of Wilno/Vilnius and Lwów/Lviv/Lvov. Part of East Prussia, which had been part of interwar Germany, was given to Poland (the other part, the Konigsberg/Kaliningrad region, became part of the USSR, and is part of the Russian Federation today), as was the free city of Gdansk. The western border of Poland became the Oder-Neisse line, which gave Poland a large chunk of what had been eastern Germany, including the port city of Stettin/Sczeczin. Also, Poland had to give back the little part of Czechoslovakia that it had taken after the Munich agreement.

Here's an OK map.

This shifting of borders had very little to do with the nationality or language of the people on the ground and quite a lot to do with power politics and the desire for stability. There were lots of Poles in the areas given to the USSR, and lots of Germans in the areas given to Poland, and they were expelled, often quite brutally. Neither the Poles nor (it probably goes without saying) the Germans were represented at Potsdam. Stalin had been very adamant about the USSR being given a significant chunk of Poland, and the western allies were not, at that point, very sympathetic to Polish demands -- and it was the Soviet army occupying that part of Europe.

As for the Baltic states, they were incorporated into the USSR in 1940 and remained part of the USSR after World War II. I'm not aware that their independence was ever on the table, although I could be wrong, and there was an anti-communist partisan movement, which received some, apparently useless, covert support from the CIA and MI6, in the Baltics that went on for an impressively long time.

Source: Potsdam, Michael Nieberg