No they're not. Tailwinds apply to the speed of sound too, thus a 200 mph jetstream raises the speed of sound in that jetstream, in that direction, by 200mph t

No they're not. Tailwinds apply to the speed of sound too, thus a 200 mph jetstream raises the speed of sound in that jetstream, in that direction, by 200mph too, and thus the speed of sound for the quoted altitude would be 961mph. The speed of sound is not just an arbitary number.