Thank you.
Raising this thread from the dead because it's been resolved.
The 14/3 version of this cable, which apparently has different shielded twisted pair makings, is in fact rated at 300v and that is printed on the cable. So after lengthy delay on my side, I sent back most of the original unused 12/3 and today got a reel with the 14/3. I paid shipping on the return and Whirlwind paid it on the new cable. I kept a 35' chunk to remind me of the experience.
The 14/3 costs less than the 12/3, so there is a bunch more cable in the exchange.
I am a happy Whirlwind customer, and am not obligated in any way to say that.