Continuity mistake: While Ali and Lisa are trying on the dresses for Sophie's wedding, after Sky leaves the room with his props, when Ali and Lisa stand up only one side of Ali's dress is over her shoulders in the shot facing Sophie, but in the shot facing Ali and Lisa both sides are over Ali's shoulders properly.
Continuity mistake: When Rosie and Donna are trying to get Tanya's boots off, Tanya is lying flat on her back. The camera does an instant cut and she is now propped up.
Continuity mistake: When Meryl Streep closes the bedroom door in the scene right before "Dancing Queen", you see Julie Walters' reflection in the mirror next to her, hands on her hips. In the next shot Streep turns to face Walthers, who now suddenly hasn't got her hands on her hips anymore. (00:34:15)
Continuity mistake: When Tanya and Rosie sit down on the boat on the way to the island, as they sit down Tanya has her hands in her lap. In the next shot they're up by her neck. (00:08:50)
Continuity mistake: When they are singing Does Your Mother Know You're Out, a man is seen getting out of water and is soaking wet. However, a few shots later he is completely dry.
Continuity mistake: Donna, Tanya and Rosie are singing Super Trouper for Sophie's Hen Party - when they get to the end of the song and all 3 ladies put their hands one of top of each other (whilst they are singing 'Like I always do') and then lift them above their heads. Rosie's hand has changed, in the first shot it is her right and in the second her left hand. (00:48:40)
Continuity mistake: On the boat when they are singing Our Last Summer, Sophie is seen sitting next to Bill. In this shot she is holding a picture of Bill in her hands. The camera cuts and now Bill is holding the photo. (00:40:45)
Continuity mistake: During "The Winner Takes It All," you first see the cliff with the church and the sun very low on the horizon. Later during the scene, the sun is much further to the right and higher in the sky (the sun glare on the water is bright white). The scene was apparently filmed in the morning (and not in the evening) and we see a sunrise and not a sunset.
Continuity mistake: When Sam tells Sophie that they could do a test to see who her father is, Sophie raises her hands to her face twice.
Continuity mistake: When Sophie is in her bedroom with Ali and Lisa after they have just arrived, Ali has a scarf and she places it on her shoulders. In the very next shot it it now suddenly wrapped around her shoulder, even though she didn't have time to wrap it around. (00:07:40)
Continuity mistake: When Donna is fixing the crack in the tiles, the tip of the filler-gun breaks off. She stands up, and a bit later waves the filler gun, with the tip back on. The pistol has been out of sight (her hands down) during the scene, but she didn't look down once, and we see that she is carrying a bowl in the other hand, so she would not have had a chance to put the tip back on again.
Continuity mistake: When Sky is getting his hat and cigar as "props" for his stag party, as he leaves the room wearing the hat and holding the cigar. In the second shot as he walks past Sophie, there is a long loose cord hanging down from the brim of the hat - which wasn't there in the first shot. (00:10:00)
Continuity mistake: By the end of the song "Chiquitita", Donna has a red rose in the side of her head (positioned in her hair) after Rosie put it in there. As the shots differ, in some shots the red rose, which should be visible (judged by the amount of the side of Donna's head we can see), is not there. It appears and then disappears a few times and is not due to the angle. (00:32:10)
Continuity mistake: At the chapel, Sam has just proposed to Donna. She says she's not a bigamist. Sam says neither is he and that he has loved Donna for the past 21 years. To his right stands Sophie, who after hearing Sam say this, is all choked up and looks like she's about to burst into tears of joy. Immediately after you see this expression we see Donna very briefly (one or two seconds). When the shot goes back onto Sam and Sophie, Sophie has a huge grin on her face. Nothing is said by Donna or Sam in this extremely brief period of time that would justify her instantaneous change of expression.
Continuity mistake: During the wedding of Donna and Sam, the rings on Donna's fingers are disappearing and reappearing.
Continuity mistake: When Donna climbs on top of the goathouse after seeing Sam, Bill and Harry, and begins to sing "Mamma Mia", as she rolls around all over the roof her dunagrees (especially the knees) become dirty. However the amount, prominence and position of the dust and dirt on her clothing changes a few times during the whole scene. (00:26:10)
Continuity mistake: When Tanya and Rosie are talking to Donna in the bedroom just before the "Dancing Queen" number, they are talking about how bad Donna used to be. Rosie then puts a hat on Donna and Tanya puts a green feather boa on Donna's shoulders - twice - between shots. (00:34:50)
Continuity mistake: When Donna, Tanya and Rosie are on the couch talking, Tanya asks Donna "if she's getting any." As she asks her this, the shot switches angles. And as it does, the towel that Tanya is wearing on her head changes from dangling behind her shoulder to suddenly hanging in front of it. (00:21:50)
Continuity mistake: When Donna breaks the shutter, her reaction is different from the angle looking into the room than it is from the inside shot. (00:16:20)
Continuity mistake: When Sam and Harry's taxis arrive at the pier, the sunlight casting on the pavement changes dramatically between shots.
Answer: Sophie finds Donna's diary from 1979, being the year Sophie was conceived meaning she was born in 1980 (as the diary entries are from July/August). So the movie is set in 2000.