They really cannot go back and change something for the previous year because of a whole host of issues. The simplest is people / businesses have already been

They really cannot go back and change something for the previous year because of a whole host of issues. The simplest is people / businesses have already been paying this years taxes under this years rules quarterly. Its already going to be a mess for software developers to rush out changes to their payroll customers for a tax plan that goes into effect some 12 days after its passage.