Adam, I found this "This is another previously unlisted quad release. By the time it was released CBS had all but given up on quad, so it was just put out as a normal stereo release." on https://dreamingspiresquadarchive.wordpress.com/2016/08/23/thjis-van-leer-introspection-3/
thanks Duncan seems kinda weird that I & II would have dual inventory release with a regular Stereo and a separate SQ LP release of each and yet the regular Stereo of III would be SQ encoded by default.. but there you go.. also, that blog has been wrong before about matrix encoded CDs (the Weather Report "Tale Spinnin'" supposedly from SQ CD was not the Quad).. anyway I'll pick up a copy of III and have a play with it thru the SM.