You are correct.
A 60,000' airburst requires an extra-atmospheric delivery vehicle. We would know the point of origin as soon as the launch was detected. 90 minutes (or less) later that place would simply cease to exist.
MAD is real.
You got it. We are capable of detectng and tracing the delivery of a nuclear payload. Any country sening one our was would cease to exist shortly thereafter. Same would happen to us if we did it to the Russians.
Thank you for understanding my point(which I thought was obvious).