SPECIAL PREMIERE: There’s a long tradition of long-running, very popular TV situation comedies presenting not only a meaningful finale, as with the record-smashing M*A*S*H, but an after-celebration special, looking back on the show’s production and history – as with Cheers, Seinfeld and Friends, just to name three. This special, Unraveling the Mystery, shows the evolution of this particular sitcom, and how Chuck Lorre and company brought it to CBS and kept adjusting its recipe. And since it and its characters evolved more than most, this is a Big Bang that more than deserves to end not with a whimper.