Before Ross and Rachel took a break, before George Costanza mastered his domain, NBC's Thursday night was big. This spring, the Huxtables, the lawyers of McKenzie Brackman, and the barflies at a pub where everybody knows your name are coming back for reunions.
•For ''The Cosby Show Retrospective'' (May 19), stars will reflect on the 1984–92 run in interviews interspersed with clips. (Lisa Bonet was the only holdout at press time.) But recollection won't be easy for all; Raven-Symone was 3 when she joined the cast in '89. ''NBC is putting together a tape to help me remember,'' says the actress, now 16. ''I remember what the floors looked like and how Mr. Cosby smelled -- like flavorful cigars and grandfatherly perfume.''
•The retirement of John Ratzenberger's Cliff from the post office is the premise for a mini–Cheers reunion on ''Frasier'' April 30. George Wendt and Rhea Perlman will be on hand, says Kelsey Grammer, whose character flies back to Beantown: ''It's like an old 'Cheers' with a lot of bar humor.'' Of the old regulars, only Kirstie Alley hasn't appeared on ''Frasier.'' (''Kirstie once said... she'd never do a show about a psychiatrist,'' says Grammer. Alley, a Scientologist with aversions to psychiatry, says she'd do ''Frasier'' only if she got to, ahem, do ''Frasier.'' She adds she's never been asked to cameo.)