Question: They say David's mom is dead because 2000 years have passed. Does David not understand that humans can't live that long?
Question: How did teddy the get extra hair? They left the room where David cut his mother's hair, and never returned. Second, how did teddy think to get the extra hair? They didn't know about DNA cloning until near the end of the film.
Question: How did they clone David's mother by using a hair sample? Hair doesn't contain DNA. Secondly, if they wanted to make David happy by bringing his mother back, why not recreate her in a simulation instead of creating a clone of her? Then David would be able to spend as much time with her as he wants.