I am trying to find a definitive answer to the question, were there any commercial matrix encoded quadraphonic cassettes manufactured during the quadraphonic era? I know that Angel records released most, but not all, of its LP's as SQ only. That is, there was no dual inventory for the Angel releases. What about their cassettes? Were the Angel cassettes remixed for two-channel stereo or were the SQ quadraphonic mixes used to make the cassettes?
I have Angel brochure "The Angel Stereo Quad Catalog" with a list of some of their albums. Cassettes are not mentioned in the brochure. Only LP records are shown. The brochure does offer this: “Packaging identification. All Angel SQ albums are identified by the Angel trademark in the double circle.” Several Angel or Seraphim cassettes I have use the double circle logo on the label, however, nowhere on the cassette sleeve is there anything to suggest that the cassette is SQ quadraphonic encoded.
Who can shed light on these questions?