I wonder if it's possible that Bill and Jamie were in Woodburry and then came to the prison.  They were both to young to battle, so it's possible.  It is also likely they would be shown in the TV series to give Hannah's sacrifice meaning, since she and T-Dog's death were similar in the fact they were already bit, their death was gruesome, and they did it to protect those they cared about.  What does everyone here think?