You may find interesting my recent blog post about how genealogical research led to the discovery of cousins who we thought died in the Holocaust. After my grandmother died, I was able to find through genealogical research what she never knew: she had two first cousins who, completely unbeknownst to her, survived the war and lived out their lives in Europe.  The post contains many searching strategies especially for Austrian (Vienna) and general Holocaust genealogy research.  https://moritzresearch.blogspot.com/2020/08/we-thought-they-died-in-holocaust-how.html

Best,
Michael Moritz (info@...)
New York