I think we had used the MFS utility at one point, where you prepare the return jointly and then split the return into 2 separate ones. That's the reason for the filenames formatting as they do, as the filenames transfer year to year. 

However, this is not a MFS return, he files single. The splitting was purely to illustrate to him how it would look if they were married. And since we didn't want to enter the data twice, I did the above.