Heathcliff and marmaduke, US of Archie.

Right away, I recognize US of Archie as a Filmation Studios series. The trick is, Filmation only had the license to produce the series; the characters are owned and trademarked to Archie Comics, Incorporated, which is notoriously stingy about their properties. Although the founders have all grown old and passed on, their heirs still hold the rights and title. The only hope that US of Archie will ever see a disc release lies in Archie Comics going bust and being dissolved. I suspect something similar applies to both Heathcliff and Marmaduke: both are comic strips owned by their creators, and printed under license by the comics syndicate. If either of these entities says nay, there can't lawfully be a disc release for either comic series.