Continuity mistake: When Wesley tells Faith that Angelus is back, she says, "Step away from the glass" and hangs up the phone. When Wesley jumps from his chair (to allow Faith to smash through the glass and escape) you can see Faith behind the glass with her hands up to her face and standing, but in the close up of Faith her hands are at her sides and she is only just getting out of her chair. (00:23:20)
Continuity mistake: When Cordy throws the knife at the door after Willow leaves, the knife hits at an impossible angle from where it was supposed to have been thrown.
Inside Out - S4-E17
Continuity mistake: The sketch of Cordelia that Angel looks at depicts her facing to her left. But once he places it back on Wesley's desk, it depicts her facing to her right, revealing a flipped shot.
Continuity mistake: When Fred is running from the oncoming white car, she runs toward a blue car getting fixed on the side of the road, but jumps out of the way as the white car hits the blue car. Fred hits the ground and rolls over to the fence, but in a following shot it shows Fred only just hitting the ground and she is on the grass, not next to the fence. (00:14:20)
Continuity mistake: When Angel and the others infect Connor with Cordy's blood, Gunn rips open Connor's shirt. In the following shots, the shirt closes and then opens again. (00:41:40)
Continuity mistake: When Jasmine picks up the car and throws it at Angel, it cuts to a shot of Angel moving out of the way then shows the car falling from the bridge. First mistake, Jasmine disappears from the shot when the car is falling, and second, the car falls directly straight and at a higher point than Jasmine actually threw it. (00:35:50)
Continuity mistake: In the season 5 episode 'Destiny' we see that the first time Angelus meets William, he has already adopted a more cockney accent, but in an earlier episode of BtVS (Fool For Love) Angelus asks Spike "Since when do you talk like that", suggesting he changed his accent after they met.
Continuity mistake: The girl being rescued at the beginning goes from standing close to the wall, looking blank in one shot, to being further away from it looking concerned in the next.
Smile Time - S5-E14
Continuity mistake: Angel is coming down the hall in the Smile Time set and he sees the trash man walking past him. In the behind shot, Angel is farther back, but when it shows the side and front shot, he's right behind him.
Continuity mistake: When Gunn is talking to Wesley near the start of the episode, he mentions that he's tracked Lindsay down, and that he's been living under the name "Doyle", and holds out the lease of his apartment. There's a close-up of the lease a few seconds later, in which the name "Lindsay McDonald" can be seen.
Answer: Everybody including Angel saw her. After helping them and then being left alone to talk to Angel, Cordelia says that the Powers That Be let her come back one more time to help them. After Angel gets a call saying that she died, he realises that it was her spirit that was helping them the entire time.