And Penny Sackett gets different results with the same data. There are different types of PRGs. There are the ones I call the Saturn types. And the floppy, sombrero type, like this one. Even finding the little beggars is not straightforward.
Apparent inclination plays an enormous role in being able to identify the silly things.
In the diagram below, we start with an intrinsic polar ring shape, and just rotate it around. We figure we'd miss about 30-40 per cent just because of unfortunate inclination.