Thanks for the correction English Bob (you weren't kidding on your site when you said you can be found hovering at most poser-related forums).
I'd noticed that some .objs intended for Poser have the normals explicitly defined and some don't (should have realised at that point!) - I'd actually scribbled down a query "f 1,2,3,4 ≠ f 4,3,2,1 ?", so I think the fact was there in the back of my head.

On the subject of single/double sided faces - I've noticed with dynamic cloth simulations that I often end up with faces from the inside of the cloth towards the camera. These, of course, are not rendered (a double-sided mesh would render correctly).
I suppose that if you created a mesh with all normals pointing outwards, then duplicated it, inverted the normals, merged duplicate vertices and exported an .obj then, when rendered in Poser/DS, it should appear as if it was a double-sided mesh? Is this the a sensible way to get over the problem?

Regarding the .pp2/.cr2, I'd already come across Kuroyume's unofficial file CR2 format spec (.pp2, etc seem to be a subset of this?). Although perhaps not quite up-to-date it seems to be a very good explanation.
Guess it's time to consider the .obj and .pp2 files together., and try adding it as a prop rather than importing it as an .obj

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The 3Dcheapskate* 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.

*also available in ShareCG, DAZ, and HiveWire3D flavours (the DeviantArt and CGBytes flavour have been discontinued).