You need to "activate" the amended return prior to making any changes....Im not sure what state a D40X is for, so Im not able to test it out and see how that one works. ....oh wait, you said DC?  Ive never even seen a DC return, sorry.

Most states you open the original return and open the amended form and input the year at the top, that "activates" it, then you go back and make the changes.