It seems like it's one of the few '80s prime time sitcoms to not have one, or at least something that was super obvious or overt. The closest thing that I can immediately think of is the one that dealt with the death of Tony's father-in-law and Sam's grandfather, Nick. This was sometime after James Coco, who played Nick died in real life.

I suppose the closest episode that falls in line with what can most categorically be considered a "very special episode", is the one where Sam gets drunk while at a frat party. Tony towards the end of the episode, gives Sam and her friends a small lecture about how they shouldn't drink and drive.