A sitcom riddle

Cast of The Wonder Years

What distinguishes the TV shows in Group A from the TV shows in Group B?
     (The appearance of the Drew Carey Show and Happy Days on both lists is not a mistake. Depending on the year, each was either in one camp or the other.)

Group A

The Drew Carey Show (one season)
Happy Days (first season)
Father Knows Best
Adventures of Ozzie and Harriet
Leave it to Beaver
The Andy Griffith Show
The Adams Family
The Munsters
Get Smart
Bewitched
I Dream of Jeannie
Gilligan's Island
Hogan's heroes
The Brady Bunch
Malcolm in the Middle
Scrubs
My Name is Earl
The Office
Modern Family
30 Rock
Mash
Cougar Town
Happy Endings
Gomer Pyle, U.S.M.C.
Green Acres
Sex and the City
Weeds
The Wonder Years

Group B

The Drew Carey Show (all but one season)
Happy Days (all but first season)
I Love Lucy
The Honeymooners
The Dick Van Dyke Show
The Cosby Show
Married, With Children
Cheers
Seinfeld
Friends
Everybody Loves Raymond
Rhoda
Maude
Frasier
The Mary Tyler Moore Show
All in the Family
Three's Company
Two and a Half Men
The Big Bang Theory
Good Times

Stumped? Tweet @AKSARBENT for a hint