Your history is your history. A selective narrow range that just includes the bulk of your best or worse years, is slanting the stat horribly. You can't be arbitrary in the stat to fit an outcome. Especially when doing a comparison.
But to satisfy your curiosity you do understand that doing our history just from 1991 until 2008 the percentage is lower than our overall history, .455. Mullen is at .606 today. That is a huge range above our norm prior to his arrival just from 1991 to today.