I worked at Vidicraft back in the 80s and dealt with a lot of these. I'm afraid that my memory is a bit spotty, though. It has been a few years!
There was a "Mono" position on at least two different products that had two different uses. One opened up the bandwidth to allow the higher-resolution b/w signal through. The other killed the colorburst signal to disable the color processing circuitry on your TV. Many black-and-white broadcasts still had the colorburst signal, which would enable the color processing circuitry on your TV. This would often generate colors in the otherwise b/w image that were rather annoying.
If my memory is correct, the Detailer II Mono position just opened up the bandwidth. Evidence of this would be noticing that color signals still pass through as color and that adjusting the Sharpness or Detail controls (probably more so with the Detail control) will significantly affect the tint and saturation of colors.
I think it was the ProcAmp that had the colorburst killer as a Mono mode. Evidence of this would be that a color signal becomes a black-and-white signal in this mode.
VNX (originally called "Core") removed low-level enhancement (the "core" of the enhancing signal). The hope was that noise was at a low level relative to real detail and that by removing low-level enhancement it would not enhance the noise yet would leave enhancement of detail. Properly used, it could be very effective. It was a specific feature that separated the Vidicraft products from competitors. Keep in mind that it did NOT remove noise from the initial signal.
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