Audio problem: Just after K finds the 6 10 21 marking on Sapper Morton's tree, he begins to head back to his car. In the shot from behind K where he is first walking to the car, the only sounds heard in the shot are his footsteps and nothing else. The shot then cuts to an angle behind the car with the door opening, and it is now shown that K has set Sapper's house on fire, and the sound effects of the flames burning are suddenly heard. The sound of the flames burning the house should have still been heard in the shot where K was walking up to his car as the house was already on fire. (00:49:15)
Continuity mistake: When Harrison Ford meets Rachael again, he says she is not accurate because "she had green eyes." But when Rachael is being interviewed for the first time in the original, her eye is displayed on the monitor. The eye is not green. (02:16:05)
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.