I believe in this case they’re either bank deposits or property in Israel (then Palestine under the British Mandate) owned by victims. It’s very similar to the various European institutions that settled a few years ago. In many cases, without a death certificate, accounts and death benefits couldn’t be claimed, after all just because someone’s father went passed through the gate at Auschwitz, doesn’t mean he’s not living the high life today in the Caribbean. In many instances heirs simply had no way of knowing what parents or relatives owned, and for decades refused to provide the identities of account, policy, or land holders. I believe most of these fall in the latter class.
Also, don't be afraid to email any of this places with questions like that. I've emailed a few research facilities and museums in reference to WW2 since I started reading books by Edwin Black. They can't offer up enough information to you. They want expanded awareness and are thorough in responses. That has been my consistant experience with 5 different places so far.