Hello Bill!
I agree with you fully about the frequency agility issue. If it's not needed for a mission function, then it could be more of headache than a feature. But then some of the receivers on AO-51 are agile and I'm not aware of any issues.
AO-51 has 4 crystal-controlled (i.e., not using PLL synthesizer in the L.O.) receivers, and one frequency-agile receiver. The frequency agile receiver was a mission requirement.
All of the receivers can be used for command operation, but the frequency agile one is so wired because it was "free" - no mass or complexity penalty. That is because the flight computer has 6 demodulators built in, and a total of five receivers on the spacecraft. It is not intended for use in an emergency recovery scenario.
73,
Lyle KK7P