Revisiting The Past

If Manse Everard stands by his decision not to visit Bronwen in ancient Tyre, then it is already the case that her later life remained untroubled by any further visit from him. Alternatively, if, at any moment before his death, he changes his mind, then it is already the case that she was visited by him. In other words, a future decision by Everard can determine events that have already happened a long time ago. I know that this is a logical consequence of the time travel concept but it is still worth thinking about. 

A criminal can be exiled to the prehistoric past and never retrieved, in which he case is already long dead. Alternatively, he could be rescued from the remote past a split second after his arrival then and could be transported to a moment a split second after he had been sent into the past. Various other tricks could be played with time. In the Time Patrol series, there is the possibility of changing past events but, even if time travellers do not do that, they have considerable scope for manipulating events that have happened and that remain unchanged but are simply not known.