I just had 2 shirts go live, and when I looked at the listing I noticed a 1-pixel white line at the very edge of the print area! The horror! So I deleted those shirts and uploaded two replacements... identical in every way except for removing that flaw in the artwork. (I made the price slightly different so I could keep them straight). I feel like leaving a note, "Yes, you just processed 2 shirts exactly like these but there was a problem with the art." Or, recently, I made some text changes on another shirt—a comment box that specifies what edits were made seems like it would help speed things along.
Of course, the ability to replace artwork on a live shirt would be helpful, or at least not have it count against my daily limit!