In the pilot episode, the back of the living room set has two windows. For the rest of Season 1, there are doors leading out of the house.
In the opening scene, there is no stairwell at the back end of the front hallway, as there is in the rest of the season.
In this episode only, the hallway on the left side of the living room has an arched opening into the dining room. For the rest of season 1, there are doors in that spot.
In one scene the Malcolm X poster is perfectly flat, but when Jeff enters the room, the bottom right corner is noticeably raised.
In the very first scene in the series, Will enters the house from the front door. Behind him there is a short brick wall. In the intro, there is an exterior shot of the house from a far angle and the short brick wall is nowhere to be seen.
Will uses a staple gun to put up a poster of Malcolm X. He repeatedly jumps towards the wall and punches the staple gun to secure the poster. Several times, the wall shakes when he hits it.
When Will looks at himself in a mirror, his reflection transforms into himself wearing clothes similar to Carlton's, with the two shots being composited together. The two shots move out of alignment with each other due to the camera not being completely still for the original shot.
When Will is stapling his poster of Malcolm X to the wall, when he first dashes over and smashes the staple gun into the poster, you notice that the wall (the set) shakes. Later on, (a few seconds later) you'll notice that the camera moves out as Will moves backwards. If you look in the top left corner of the screen, you'll notice it's showing a bit from outside the set. The camera then quickly moves down to cover it up.
In the opening scene when Will is doing his mockery of Geoffrey, the mirror over his right shoulder shows crew or equipment moving.
In the first scene when Will and Vivian is sitting down on the couch, you can noticeably see an boom mic on top of the frame.
In the pilot episode, Will's character is 17 years old and Ashley is only 9. By a few episodes into the second season, Will is still only 17 yet Ashley has aged to 13.
Ashley spells Will's name with only one 'L' on her painting.