IRS is going to delay the refund for a few months regardless of what you do, so go ahead and guess in favor of the client so that there is something on the return to adjust.  Commissioner Rettig just patted himself on the back for five pages of blaming everyone else for causing return processing delays while his people make heroic efforts -- to correct mistakes that would not have occurred if they had just left the data available on "Where's My Payment" a few months longer.