Continuity mistake: The layout of Frank and Carol's house is inconsistent with the exterior shots. The driveway as seen from their backyard is more shallow and narrow than what is shown in the exterior shots, and the stairway to the left of their front door has a window halfway up, but the exterior shot shows a low section of roof that would completely obscure any window.
Torn Between Two Mothers - S5-E14
Continuity mistake: At the end of the episode, Frank is talking to his mother in the kitchen, and she sits down at the table. The green jacket on the chair behind her keeps changing positions between shots.
Continuity mistake: In this episode, Steve Urkel appears, depicted as a real person. But Urkel also appeared in a few episodes of Full House, which, within the universe of Step by Step, is a fictional television series.
Continuity mistake: In season 1 Dana turns 16, then in season 3 she is 18, yet they are only celebrating their one year anniversary.
I'll Be Home For Christmas - S4-E12
Continuity mistake: When we see JT arriving at the ski lodge in his car, it appears to be the same car he bought in an earlier season and had to sell for parts.
Answer: I could be mistaken, but when the series debuted, its premise was something along the lines of "A divorced contractor and a widowed beautician impulsively marry." If that is true, then the Foster children's father is dead. As for Frank, it could be that his wife was an unfit mother and is therefore not in her children's lives. Perhaps the writers felt addressing these issues would lead to more questions, or at the least require characters to bring up the unseen parents more in conversation, so perhaps they felt it was just better to never talk about them at all and let any discussions about them remain off-screen.
Phaneron ★