indeed, the disc inside both the SQ sleeve and the Stereo sleeve could well be the same.
that said - and i realise its a different album and artist altogether - but fwiw another Dutch LP with a dual inventory SQ Quad counterpart, is that "Swinging Marches!" disc I posted a pic of here the other day.
now, interestingly, I have both the CBS Dutch SQ version and the CBS Dutch Stereo version and having briefly compared the two, the disc in the SQ Quad marked sleeve sounds different to the Stereo LP of the same album. when i get a chance i will compare the two versions and have a look at the individual decoded channels of each disc and check out some waveforms, etc.
good idea! i'll get someone technical to look into it.
failing that, i'll have a non-technical look when I pick up a copy of the Introspection 2 CBS 65915 disc and see how I get on comparing it to the Q 65915 LP.