In the Fisher and Japanese designs, this resistor forms a divider with the feedback circuits (both positive and negative) to determine how much feedback there is. In the Fisher circuit, the feedback is brought directly to the junction of the cathode resistor and the ~ 200 resistor you mention. In the Japanese circuit, the main cathode resistor is bypassed by a cap for AC signals. The feedback is applied to the top of the cathode resistor, but since it is bypassed, again, the 200 ohm resistor becomes the other half of the divider. In the third circuit, there is no such resistor, so the 680 ohm cathode resistor becomes the divider for the feedback circuit as well as providing the usual cathode resistor function for the tube.
Dave
Dave