That is unusual. Would Dragnet also qualify?
The 1967-69 shows vs. the 1950’s shows? I’m wondering what other spinoffs occurred years later......
I'd say that Dragnet might be more like the second pass of The X Files, or recently Heroes - just continuing the story where they left off, just years later. Maybe even throw in the second pass at Dallas with Larry Hagmans, Patrick Duffy, and Linda Gray. They even kept the same theme song.
-PJ