I have the following "As of" expression that is not showing the accumulation of the payment amount after the period when the payment first happened in 2012-Dec. The set analysis syntax has a search parameter to include all payments on or before the Max([Year Month]). In this case the Max([Year Month]) is 2018-May.
The expression I am using is numeric. However, to confirm if the "Year Month" was the issue, I changed the expression to the following. The change did not correct the issue. Please see attached screen shot of the table using the new expression.