Can I just check that PC’s assigned to either variations or song parts will be received on any channel? That is, a channel is not specified (unless assigned in Settings for Song Parts)?
Why is this is, if PCs can be sent to GP on specific channels?
Thanks 
Obviously not! Thanks 
By the way - is there a reason why this is only a global setting and not per variation/song part (like all the widgets, or the song part MIDI assignments themselves in settings)? How would GP differentiate between PC’s sent by two different keyboard controllers for example?
As far as I can see, GP can’t differentiate. You can only limit to dedicated MIDI ports (i.e. allow specific boards), a single channel, and additional information like Bank Select MSB/LSB
What’s your use case?
For me personally this would be hell to derive different PCs from different devices…
I typically use a setlist tool like Bandhelper and let GP ‘translate’ and switch/send MSB/LSB/PC to additional external gear (if needed)
Use case - sending PCs from TouchOsc. Not a dealbreaker, just interested.
If you have a hardware synth that respond to program changes, it’s not going to respond to them differently depending on what device sends them.
I don’t understand why one might think that GP should respond differently depending on the sending device.
The reason we have a mechanism to allow GP to respond on a single channel is because some multitimbral workstations send out program change messages on multiple channels and one obviously doesn’t want GP changing rackspaces multiple times as a consequence.
If you have touchOSC then you have more sophisticated options using OSC messages instead of PC messages.