Tonight I confirmed that the two RF switches are working properly. They are not at all sensitive to the actual voltages put onto the control pins, anything between a few volts up to 14V enabled the switch. Anything from -1V down to -5V turned the switch off. That's as far as I dared to test. When the control input was floating (0V), the switch let through the signal with some 35dB attenuation. An "off" switch attenuated some 70dB (down in the noise of my spectrum analyzer).
I also found out that the 08415-60057 number printed on the RF switches is the HP part number. Apparently, over the years, there have been multiple models of 18GHz and 20GHz switches, from multiple manufactures, that have been marked with this same HP part number. So, it is possible that the 1699 model (which I don't have a datasheet for) may actually require a higher span on the control voltages than the 2677 I found a datasheet for.
So, now I will continue checking the downstream modules (A68 attenuator and A53 mixer) per the previously attached block diagram. I'm now more confident that the control voltages of -4.62V and +13.18V may be correct (although not per the 2677 RF switch dataheet).