Anyhoo, I’m not an expert on refrains, but I think your comments make sense. The union organiser model you describe has a clear agenda and possibly an outcome that’s only really visible to one party. And it’s not really open to modulation, which means that it’s not (on its own) a refrain, altho’ it could form part of one.

And I love your bit about the relation between channels and flows. Damn you! I needed something that succinct a couple of days ago. Ah well…