CNN —If all shows were animated like “The Simpsons,” networks wouldn’t need to strain to keep them alive. Yet live-action dramas come with shelf lives, which explains the CW’s twin attempts to extend two of its franchises with prequels: “Walker Independence,” a back-to-the-Old-West adjunct to its Texas Ranger reboot; and “The Winchesters,” a one-generation-back rekindling of the “Supernatural” flame. The main problem with “Walker” is the events that set the show in motion feel much better tailored to a limited series than an open-ended run. For now, “Walker Independence” (which, yes, will follow “Walker”) and “The Winchesters” come blessed with name recognition, but creatively speaking, first impressions say that the network has dipped into the prequel well twice too often. “Walker Independence” premieres October 6 at 9 p.m.

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