[deleted orig. questions]
I just learned that Live responds to a MIDI CC [example, MIDI CC# 104], when mapped to trigger a clip, only if I send a CC value of 64 or greater.
If I program my MIDI pedal to send MIDI CC#104, value 63, Live ignores it when #104 is mapped to trigger a clip.
Sheesh, I wasted more than an hour trying to find out why Live was letting me map a MIDI message, but then refusing to actually do anything once I mapped it. Hope this saves someone the same trouble.