September 17th, 1939 was the day of the Soviet – Red Army invasion against Poland. On that day the German Nazi and Soviet Russia alliance was forged in common fight against central European countries and most shockingly against their civilian populations. The two totalitarian state ideologies unexpectedly allied till June 22, 1941, started to execute the lethal policy of social cleansing over the dead body of central European countries. Civilians became a major target for the first time in history of European conflicts.
If your family fled east in early September, which was the natural instinct to run from the German Army entering Poland, then very likely they will be traced and registered by the Soviet security apparatus NKVD. There is a very good database developed within 1988 and 2013 by Archiwum Wschodnie and KARTA showing the NKVD documents on Polish citizens interned or deported. Unfortunately it is a bit rigid to use, as from 2013 it is administered by IPN and its development was abandoned.
This day makes me think about the Russian historians from institutions like
who risked and still risk a lot for historical truth in the times of dominating politics of memory in service of current politics.