Left Behind - S3-E10
Continuity mistake: In the previous episode Ra's al Ghul stabs Oliver through his chest, just below his left pec. When he pulls out the sword, a wound is visible. (However, seconds later, the wound is absent - different mistake). In this episode he is shown with a wound much lower (in his lower abdomen) and also later, with a bandage around his waist instead of his chest. (00:09:30 - 00:41:30)
Factual error: The highest-ranking military officer in the DIA (Defense Intelligence Agency) is the director, which is a three-star position. John's stepfather Roy Stewart would not be a part of the organization, let alone answering to superiors in the organization if he was a four-star general.
Left Behind - S3-E10
Visible crew/equipment: During a flashback with Oliver and Maseo, they are on a rooftop trying to break in to the building next door by means of the pulley system on the bow. Maseo is shown lining up a shot with his sniper and in the background one can see a crew member's face looking over his shoulder. (00:13:30)
Suggested correction: There are other ARGUS agents with Oliver and Maseo. That is one of them.
Continuity mistake: Oliver chops off Malcolm's hand to end their duel. When Oliver hands the ring over to Nyssa you can see Malcolm lying in the background where he has been cut down with two hands intact, and the cut off hand nowhere in sight.
Blood Debts - S4-E10
Continuity mistake: When Conklin is whipping Oliver during an island flashback, the wounds from the whipping are visible, but after Oliver threatens to shoot himself unless Taiana remains unharmed he hands the gun to Reiter, and we get a good look at Oliver's back, wound-free.
Continuity mistake: Yao Fei takes the bow away from Oliver in one shot, then Oliver hands it to him in a following scene. (00:02:10)