Dragnet: PD or not PD?

[See our update on this entry] 
Dear Rich: Who owns the rights to the Dragnet TV series from the 1950's? I understand it was owned by the Jack Webb estate after he passed away in 1982. I am trying to find out if the original prints or negatives of these shows are available to be put on DVD or Blu-ray. I know that the copyright for some shows has run out but the copies available are old 16mm TV prints, I am interested in the 35mm originals. Some (or all) of the 1950's series episodes of Dragnet appear to be in the public domain, probably because of a failure to renew the copyright. According to our friends at Wikipedia, "Most, if not all, episodes of this [1951] series have become public domain, and fifty-two episodes have been released by many DVD labels." The public domain status is reinforced by the fact that 64 episodes of the 1951 series are available at the Internet Archive. Because there were 276 episodes in the 1951 series, its not clear why the remaining episodes aren't available. Either: (1) they're not in the public domain, (2) Mark VII Limited (the production company that owns the shows) has never released them for distribution, or (3) copies of the episodes don't exist anymore. (BTW, the 1967 series is under copyright.) (Previously, we wrote about the public domain status of the Dragnet theme song and radio show. )