I have the 6 7 8 9 W irons, the 6 7 8 weigh 233 grams while the 9 W weigh 255 grams, questions?

 

Would the heads 6 7 8 being the same weight take same length shafts work better, and why are they the same weight? Was this the norm for Nickent, I’ve checked the weight lots of times…