Interesting observation, Jim.
I had corresponded with a chap who for years built custom arrows for competition shooters. He'd go to shoots (both wheel and stick)and peddle his wares. Those big money boys wanted perfection.
He spined and weighed every arrow. His observations were, regardless of the money, that nearly all carbon shafts, sold by the dozen, had at least 1 or more that were 'off'.
He kept separate boxes and eventually would get a matched dozen even of those which were "off".
True, you can't actually MEASURE spine of carbon on a static tester, but you can check consistency among shafts of the same pack!
You found different than he. Carbons are my choice of shafting, but the more I read, the more I'm convinced they have to be monitored as well.
My last dozen had 3 that in individually tuning, showed a slight variance... but everyone's mileage may vary...