Continuity mistake: Joey states he has never lived alone. Yet in "Friends," he had his own appartment.
Other mistake: In season one when Alex got divorced, Joey and Gina talked about how Gina got divorced from Michael's father while she was still in high school. In season two, we learn that Jimmy is Michael's father. Joey didn't even know that they were together, he certainly would have known if they were married.
Other mistake: How on earth can a jobbing actor in a late-night soap with a non-paying tenant afford a huge, luxurious, two-bedroom apartment, complete with balcony and communal hot-tub, all within a few miles of the Hollywood sign? That's the expensive side of L.A, and he'd be very lucky to get that apartment for under five figures a month.
Plot hole: In the episode where Joey tells Jimmy that Michael is his son and they cut of some of his hair to do a DNA test, Gina tells Michael that he is missing some hair on the back of his head. In the next shot the angle changes, we can now see the back of Michael's head, and he's not missing any hair.
Continuity mistake: Episode 1-19 Joey and the Fancy Sister. When they are looking at the engagement ring under the black light, the ring goes from Joey's hand to Gina's instantly between shots.
Continuity mistake: As Gina walks around the pool, you can see the soles of her feet are dirty, she then lies down next to Joey, and they are clean.
Episode One (a.k.a. Joey and the Student) - S1-E2
Continuity mistake: During the scene when Joey and Michael go to Gina's after she got them kicked out of the bar, the cork in the wine bottle appears and disappears from the bottle. (00:13:45 - 00:14:20)
Episode One (a.k.a. Joey and the Student) - S1-E2
Continuity mistake: When Michael and Joey are Gina's house, when Gina is talking to Michael about changing her ways, the shoulder of her top keeps changing positions on her shoulder. (00:14:40)
Episode One (a.k.a. Joey and the Student) - S1-E2
Continuity mistake: In the scene where Michael asks Joey and Gina to leave the bar, when Joey has gotten up and left and Gina is looking in the mirror, her pink handbag is in her right hand. Yet when the shot changes it is suddenly is in her left hand. (00:20:55)
Continuity mistake: Just after the opening credits, when Joey runs out to see Jake, Jake has one hand out in one shot and then puts the basketball in both hands. When the shot changes, his hand is out again and then he puts the basketball in both hands again. (00:04:15)
Continuity mistake: When Michael is talking about Seth's girlfriend, Joey has a board of cheese and grapes out. When the shot changes, the grapes have disappeared off the board. (00:05:35)
Continuity mistake: At Joey's party, when Alex and Michael are talking about Seth's girlfriend, the food on Alex's plate keeps changing places in between shots. (00:10:00)
Suggested correction: The plate is just turned around... The food does not changes.
Continuity mistake: When Joey and Howard are clearing up after the party, we see that Joey throws all the rubbish he has in his hands in the bin, yet when the shot changes he has more to throw in the bin. (00:20:30)
Revealing mistake: When Joey is climbing the wall, you can see that the piece of wall he breaks has a break line in it.