Okay, don't shoot me now ... but I think you might be able to do this without creating a whole definition and evaluator for this column.  We already get the data for the sort column somewhere else, but we need it to be converted to 'yyyy-MM' in order to be sortable, right?  So, let's use a `DateConverter` and reference the original definition in the column configuration ... e.g.

`dsd.addColumn("Year Month Sorting", dateARTStartedDataDefinition, nullString, new DateConverter("yyyy-MM"));`

This should do the same thing.  Can you try it and see?