Gene, W4SZ wrote:
"However, the physical entities do not have two values at once in the
same time and place."

You can measure each of the two simultaneous constituents with the right
equipment. A Bird Thruline wattmeter uses a directional coupler to
separate forward direction power from reverse direction power. These are
obbtainable at the same time and place anywhere in a 50-ohm coax line.
Individual volts and amps in each direction are easily calcuable from
the powers indicated in each direction.

Best regards, Richard Harrison, KB5WZI