To be safe, you should span more years than you think are necessary. For example if your client states they are unfiled or owe from 2006, you should begin earlier and span to at least a year past the current year. For example in this case you may put 2003 through 2016 on the form. This would cover everything that is still within the 10 year statute and a few additional years in case there are unfiled returns or new issues arise in the future.