Continuity mistake: When K is smoking a cigarette in his apartment, he blows the smoke towards Joi which passes through her. K then lowers the cigarette to his lap, and some additional smoke can be seen emerging from the cigarette at the bottom of the shot. The shot cuts to K beginning to move his legs, and the additional smoke has vanished. (00:18:25)
Continuity mistake: When K and Joi are talking at the apartment after K returns home, Joi picks up the Pale Fire book and K tells her she hates that book. Behind K's head is some smoke from the cigarette he smoked when he is saying the line. Joi then says she doesn't want to read either, and the smoke behind K's head has disappeared. (00:18:45)
Continuity mistake: When the LAPD are looking over the bones, there is a shot of the teeth from the skeleton being placed on a table one at a time. The shot cuts to another angle of the table to focus on the hair sample, and the part of the table where the teeth have been placed is still visible in shot, but the teeth are suddenly nowhere in sight. (00:24:05)
Continuity mistake: When Coco is examining the skeleton, the shots of Coco in focus show Lieutenant Joshi in the background leaning her elbow on the medical table, and remains this way until Coco says "Sorry" after referring to Sapper Morton as a sentimental skin job. Joshi then asks where's the kid and she suddenly has her arms crossed and not leaning on the table. This isn't very easy to see when she is asking, but is noticeable when Coco gets up from his seat in the next shot. (00:25:35)
Continuity mistake: After examining the skeleton, Coco gets up from his seat and K starts to walk towards the console to examine the skeleton himself. When K begins to walk over to the console, Joshi has her arms by her side, but in the next shot, her arms are suddenly crossed. (00:25:50)
Continuity mistake: When K is getting out of his car after the scavengers break the door open, he struggles to stand, holding onto the side of the car. One of the scavengers then runs up to K, next to the car. K then fights back and he is suddenly standing upright, several meters away from the car. (01:02:45)
Continuity mistake: When K is ambushed by the scavengers, the first one attacks him and K breaks his back with his knee. A second one then attacks him and K drops the first. When the first is dropped, the body is positioned near the car. Seconds later, when K is blasted back by an explosion, the first scavenger that attacked K has moved more ahead of the car. Also, when Luv is shown watching K from her perspective, the first scavenger's body has now moved again, several meters away from the car. (01:02:50 - 01:03:50)
Continuity mistake: When K fires at the scavengers in the scrap yard, he keeps his gun pointed at them and an additional group of scavengers runs over a hill in the background. The shot cuts to an angle behind K, with his arm lowered, but in the next shot, his arm is suddenly raised and aiming again. (01:03:00)
Continuity mistake: When K is visiting Dr. Stelline in her facility, he has a bloody bruise next to his eye and eyebrow. This remains on his face for most of the scene, but when Stelline tells K that we recall memories with our feelings, the bruise has disappeared. (01:19:40)
Continuity mistake: Dr. Stelline offers to analyse K's memory to see if it is real. She sits down on a bench where her console is shown and is smiling with her mouth closed. K then sits down on a bench on his side of the glass. When this happens, Dr. Stelline's reflection can be seen in the glass, and she is now smiling with her mouth open. (01:20:15)
Continuity mistake: When K arrives at Dr. Stelline's facility with Deckard, his left ear is visibly mangled and injured. At no other point in the movie or in any prior scene, did his ear have this damage done to it. It just appears in this scene out of nowhere. (02:29:10)
Continuity mistake: When K frees Deckard from his restraints after drowning Luv, K pulls Deckard out of the water with his right hand, grabbing onto Deckard's shoulder. In the next shot, K suddenly has his right hand on the ceiling of the car. (02:25:45)
Continuity mistake: When K gives Deckard the wooden horse, he tells him "all the best memories are hers" whilst looking at him, but in the next shot, K is suddenly looking at the wooden horse. (02:29:00)
Continuity mistake: In the sinking car, when K frees Deckard from his restraints, he pulls Deckard so he is above the water. Deckard has his left hand above the water when he is pulled out, but in the next shot, his hand is suddenly below the water. (02:25:45)
Continuity mistake: When K hands the hair sample to the clerk at Wallace Corporation, the clerk puts down the note with the serial number for the replicant, and places it on the desk, with part of it positioned in front of the keyboard. From another angle, the note cannot be seen. This could not be due to the clerk's head blocking it, because the note was placed in front of the keyboard, and the keyboard is fully visible in shot with no note visible in front of it. (00:29:45)
Continuity mistake: Lieutenant Joshi is talking with K in her office, instructing him to kill the replicant child, leaning against a window. After K says "To be born is to have a soul I guess", Joshi replies "Are you telling me no?", walking away from the window. K then says he wasn't aware that was an option, and Joshi is suddenly leaning against the window again. (00:27:55)
Continuity mistake: When K is fighting Deckard in the casino, after K throws Deckard onto the couch, K tells him "Look, I don't want to hurt you", and extends his right hand, but in the next shot, he is extending his left hand. (01:49:30)
Continuity mistake: In the casino, when K and Joi hear an alarm going off, K lifts his hand up and switches off the emanator, but in the next shot, his hand is suddenly back in his lap and the emanator has disappeared from his hand. (01:57:40)
Continuity mistake: When K and his girlfriend are talking about a real boy name for the protagonist, as the camera cuts from one character's face to the other's Ryan Gosling's hands are holding up his chin in some scenes and in others they aren't. (01:15:00)
Continuity mistake: When Dr Stelline offers to look at K's memory, she begins to remove the lanyard around her neck that is connected to the device she is using. In the shot where she begins to take it off, her left hand is positioned above her right shoulder when the shot ends. When the shot cuts, her left hand is lowered to her side. (01:20:13)
Answer: Think of any manufacturing process. Samples of new products are frequently created and then immediately destroyed. Also, the new replicant would require processing, training, etc. It was simpler for him to just dispose of the test.