My guess is they are intentionally the same ball, however small variances in the chemistry between production runs can cause slight changes in ball reaction. Its probable they tested balls with different colours and the different pigments affect the hardness of the coverstock.
OR
The human error of perceived difference. I'm not sure how they arrive at those numbers but I would guess it is pretty hard to be absolute with it. Perhaps the lane condition has gotten drier over the 2 years?
Edited on 7/4/2008 4:53 AM