{geni:about_me} Birthdate is found in Geburtstags Merkbuch / Birthday Book of Ernestine Reif Schlesinger, in possession of Janet Lindner, ERS's great-grandaughter. Entry by Ernestine Reif Schlesinger, his aunt.

Hans Popper b. Nov 5, 1898 appears in the list of those who were forced to declare property / had bank accounts which is at http://www.avotaynu.com/holocaustlist/p2.htm. The list is "a database of 50,000 Holocaust-era Jewish names."