I'm fairly certain that you didn't have to go to the effort of using a trust account (which should be relatively simple to create) because your funds were in private retirement accounts which would show a clear history of deposits over time and/or any previous withdrawals, not in regular savings or checking accounts.My wife and I applied for a pensionado visa from the US at out city's Argentine consulate in 2016. While we were retired already, we were not receiving SS benefits and did not have pensions per se, just private retirement accounts. For that reason they said we would have to give us a rentista visa. They did not require that any part of that money be put in a trust
That being said, it might be possible to qualify for the visa rentista if the $40K USD are invested in certificates of deposit with varying maturity dates that will generate the required monthly funds to satisfy migraciones...at least enough to issue a via rentista in this case.
If not, a simple trust account (with the funds in the trust invested in certificates of deposit with varying maturity dates) should make them happy.
PS: I imagine migraciones will want to know the source of the $40K ali84747 hopes to use to qualify for the visa, and acceptable detailed records of the source of the funds could be very important if they ask.