They could be that stiff. I test mine on a RAM spine tester that is made for carbon shafts. It is set up at 28" with a 1.94# weight. I shoot Gold Tip shafts, 55/75 (which are marked .400 on the shaft). I have tested upwards of 30dz of these shafts and NEVER ONCE had a shaft spine out at .400. The are all stiffer, with most being between .350 and .380. There are also oddballs that are as stiff as .310, and as weak as about .390.
That's all I can tell you about it. I don't know why it is that way. You would think they would be a bit closer to what they are marked, or would be marked a bit closer to what they actually are?
Bisch