Based on how much Mary, John, and Alice have also done in their small lives, it's probable that while they were still alive, one of Tom's clones gave the three access to the cloning machine without the real Tom knowing.
Basándose en todo lo que han hecho Mary, John y Alice en sus cortas vidas, es probable que, mientras vivían, uno de los clones de Tom les dejara acceder a la máquina clonadora sin que lo supiera el verdadero Tom.