Easton, and most other carbon shaft manufacturers, doesn't use the same parameters for measuring spine as those used for measuring wood shafts. The carbon folks use a 1.94# weight and measure the spine in the center of the shaft between two posts 28 inches apart. Wood shafts are usually measured with a 2# weight on posts set 26 inches apart. The First method yields a considerably higher spine. For example, an Easton carbons shaft spined .40 is 72#; .40 using the 2# weight at 26 inches is 65#.
Regardless, the shafts within a particular spine rating should be pretty close to one another. It's pretty easy to get wood shafts spined within 5# of one another. Carbon should be able to match that, though apparently that's not always the case. Regardless, most folks can't tell the difference in 5# of spine anyway.