In an early 1992 episode, Johnny Galecki played Mark's younger brother, Kevin. It was later in the same season that his character's name changed to David. In season six, episode sixteen, "Everyone Comes to Jackie's", during an argument with Dan over David and Darlene living together in Chicago, Roseanne states that David isn't even his real name, Darlene just made that up. Which may explain why he was Kevin in the earlier seasons and David in the latter.
In "Brain Dead Poet Society," Roseanne only serves a plate of food to Dan and Darlene, but DJ and Becky have plates of food in front of them at the end of the scene.
Final Episode - Final Scene "Those who dream by night, in the dusty recesses of their minds wake in the day to find that all was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes, and make it possible." T.E. Lawrence (Lawrence of Arabia)