This falls into the category of  "Short Little Man With a Green Eyeshade" question.  It assumes there is someone at IRS - actually, thousands of them -- scrutinizing the year-to-year filing habits of millions of Americans.  Or, that Congress gave IRS billions of dollars five years ago so by now they have installed the best of AI software to spot situations that in the end have a perfectly normal explanation.  

In the words of the great mariachi artist Jose Alfredo Jimenez, "Estas cosas en la vida que parecen increíbles se repiten diariamente."  These things in life that appear incredible are repeated daily.