Border collies: explain these whistle signals?

[Pork_Rind]

@Machine_Elf

This seems to get at an important part of what I was wondering when I wrote the OP. So it’s not “Jeff, flankleft” and “Jim, flankright” - it’s more like “Jeffflankleft” and “Jimflankright”, with the whistles being distinct enough so that Jeff and Jim don’t interpret whistles not meant for them as anything other than gibberish.

My understanding, based only on dim memory of something from television, is that dogs working together understand the whistles for the other dogs; they’re not gibberish to them. In fact, the smarter dogs use that understanding of what the other dogs are being asked to refine their own action.