Other mistake: Kara never has enough room to wear the super suit beneath her clothes.
Continuity mistake: Before Kara uses her heat vision against Vartox she gets some dust on her suit, then she stands up and the dust is gone.
Continuity mistake: When Vartox starts to fight Kara the sun changes between shots.
Continuity mistake: When Vartox attacks Kara from behind the background changes in the next shot.
Continuity mistake: While Kara is fighting Reactron at the junk yard the sun on the floor keeps changing.
Continuity mistake: Livewire has part of her hair over the front of her right shoulder. A shot later after discovering her powers suddenly her hair's over the front of both shoulders.
Character mistake: When Kara breaks her arm, she says that she doesn't need to go to a hospital because the bone will heal when her powers return. She would still need a splint or a cast to ensure that the bone sets in place properly; leaving it untreated runs the risk of a physical deformity or other unforeseen complications down the road.
Factual error: After his father escapes from prison, Winn is interviewed by the FBI. Escaped fugitives fall under the jurisdiction of the Marshals' Service.
For the Girl Who Has Everything - S1-E13
Other mistake: In Kara's hallucinations of Krypton, the planet is shown with a yellow sun. Rao, the supergiant around which Krypton orbited, was red.
Continuity mistake: When Alex brings donuts to try to convince Kara to come back to the D.E.O., Kara picks up 2 donuts which suddenly change to 1 once she sits down, and then back to 2 a few shots later in a wide shot.
Visible crew/equipment: When Winn is putting on his shirt after being caught, you can see his mic wire through the hole where Kara says he forgot to button his shirt. (00:03:15)
Continuity mistake: When Cat is on the talk show, the microphone on her collar keeps disappearing and reappearing between shots.
Factual error: The Marine Colonel in Supergirl played by Eddie McClintock spends all of his time wearing Marine Officer's Dress Blue Bravos. Marine Dress Blues are ceremonial uniforms. On rare occasions, the Charlies or Deltas (no coat) may be worn as a work uniforms (the primary exception to this rareness being recruiters). The full uniform is certainly not worn for day to day work in the field.
Continuity mistake: While Kara and Alex are on the beach the sun on the floor changes between shots.
Continuity mistake: The bottom circle on the left drawn by Barry on the whiteboard changes shape between shots.
Continuity mistake: While Kara is on the ground after livewire hits her with electricity, the sun changes between shots.
The Adventures of Supergirl - S2-E1
Continuity mistake: When Kara saves the chopper the sun on the floor changes between shots.
Continuity mistake: When J'onn J'onzz is fighting Miss Martian in the ring, she punches him into a wall, leaving a massive dent. She missed the next punch, and the plaster on the right hand side of the dent falls out, but the plaster on the left is fine. Miss Martian then throws J'onn across the room, and in the background, the dent is visible, but it is now the left hand side of the dent where the plastering is missing and the plastering on the right is now mostly in place.
Continuity mistake: Mike and Kara are in the alien bar in the both talking about Mike not controlling his powers. When Mike breaks the glass there is no other glass on the table. In the next shot a glass appears at the edge of the table, in the next shot the glass is gone again. (00:03:30)
Continuity mistake: Maggie comes to Alex's apartment with pizza. When Alex opens and closes the pizza box, she folds the pizza box edges in and 3 shots later the edges are outside of the box.
Answer: For one, it's usually cheaper to film in Vancouver because of the tax breaks. But all the CW Arrowverse shows (with the exception of "Black Lighting") are/were filmed in Vancouver. So it makes it easier and cheaper for sharing set designs, crossovers, etc ("Black Lightning" filmed in Vancouver during its crossover). Originally "Supergirl" wasn't part of the Arrowverse when it was on CBS, but it was too expensive to produce and wasn't reaching the wider audience the CW shows had. So CBS moved it to its sister company, The CW.
Bishop73