This might sound funny: There has at least been one episode where each cast member didn't appear in:

1. The vegas episodes, Jackie doesn't appear.
2. Even though a member of the cast, Crystal didn't appear a lot in Season 4.
3. Lecy Goranson appeared in four episodes during season five.
4. DJ wasn't in three episodes in that season (Nancy's a lesbian, Arnie returns, Molly and Darlene go to the rock concert.
5. In season 6 and 7, Darlene appears in like every other episode, as well as Becky (if you notice in Jackie's house, there's a picture of the old Becky and Mark on her book shelf. It's clearly visible in the Season 6 and 7 shows.)
6. The second episode of season 6, none of the kids appear.
7. In season seven, part one of the flashback, Roseanne doesn't appear in the new scenes. She also doesn't appear in the episode where Jackie was seeing another man.
8. In season 8, Sarah Chalke and Lecy Goranson alternate the role of Becky in three episodes. (If anybody knows why, please let me know.)
9. Season 9, Dan, Darlene, and Becky appear in like a handfull of episodes. I think Becky really only appeared in like 6 episodes.

That's kind of weird and nice to hear that they actually had a picture of Lecy in the background when she had left the show and Sarah was now the Becky character.