Interesting thread. I was really confused about circular polarising filters. Being a radio ham I knew what horizontal, vertical, and circular meant. I had used aerial with both clockwise and anticlockwise circular polarisation, but with camera filters in fact circular was not really circular but a linear filter with a 1/4 wave filter sandwiched to it and was not really a circular polarising filter. So the statement "Unlike linear polarizers, you don't have to turn circular polarizers" is true but what we call "circular polarizers" are not really "circular polarizers" but a linear polariser and a 1/4 wave stuck together.

As to how many of the others are due to poor description I don't know?