Thanks RedPhantom. I just reran Poser 11, imported the two OBJs (pole and streamers, exactly the same ones as before), left the pole as a prop, clothified the streamers using a single dynamic group, but this time put the top pair of vertices of each streamer into the choreographed group as you suggested - Remembering to remove those vertices from the dynamic group, something I may have overlooked before. Those top vertices are inside the mesh of the pole as before, but that didn't seem to cause any problem - the simulation calculated at a reasonable speed. Screenshot of the top pairs of vertices in the prop pole setup, overlaying one with other objects hidden on one with them visible.

However, it refused to play, exactly as before. So I saved it as a sensibly named PZ3. Still refused to play. No sign of any abc file, just the PZ3

Restarted Poser, loaded the PZ3. Still refused to play.

Reran the simulation, and noticed that as I did this the abc file appeared. Now the simulation replays as it should.

So it appears that I have to save the scene before calculating the simulation.

Another oddity: putting the top two vertices into the constrained group, which is what I did when the pole was a figure, didn't work when the pole was a prop - the streamer tops just extricated themselves from the pole and fell to the ground

I was planning to have the bottom two vertices of each streamer in the choreographed group, and planning to do something clever with simple morphs to get that clockwise/anticlockwise under/over weaving of a typical maypole dance. The top was going to be held in place via a constrained group. But I think I have an idea that might work with them both in the choreographed group...

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.