I apologize as I'm guessing this must have been addressed before, but searching back is very tedious and time consuming. I'm looking to upgrade my irons to newer, but not brand new clubs. Many club manufacturers don't come out with a new line of irons every year but release on two year cycles. Combing through the Most Wanted articles I've noticed that in some cases, such as with the Titleist 918 irons but others as well, the performance rankings given in the Most Wanted write-ups sometimes vary considerably from the first year to the next, either greatly improving the second year compared to the first, or significantly worsening. Is that most likely due to changes by the manufacturer within the product cycle, changes from year to year in the testing methods and performance criteria, or the vagaries of a changing mix of those who swing the clubs from one year to the next? Thanks.