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: 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.
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: 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.
Continuity mistake: While Kara and Alex are on the beach the sun on the floor changes between shots.
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: While Kara is fighting Reactron at the junk yard the sun on the floor keeps changing.
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 Cat is on the talk show, the microphone on her collar keeps disappearing and reappearing between shots.
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.
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.
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.
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