Replying to Full tilt flex index

I thought I understood this system. I just ordered a pair of 8's to replace the tongues on my seth morrison's because they were pretty stiff. I just opened up the package and the dial on the tongues is pointed to four, and I just took off my old tongues and they say "flex 8 index" so is there a difference between flex index and the number it says on the boot? I thought the seth morrisons were supposed to come with 10s. So I'm guessing they sent me the wrong tongues in the mail.

I don't ski park at all, and I weigh about 125 will I find any use out of the 4s or should I just return them? I guess if I've been skiing 8s and those feel a little too stiff maybe 6s would be good? I ski resort, powder, and big mountain only.