To put my previous post in terms of Terry's original domino analogy, there are two timelines:
State 1. The dominos at time A in an arbitrary configuration.
State 2. The dominos at time B (dominos from time A at a later time in the future in a configuration descended from time A).
If the dominos from state 2 go backwards in time to state 1, then it appears from the perspective of the state 1 dominos that duplicate dominos have appeared out of thin air in a different configuration, basically being in two places at once and violating the premise there are a finite amount of dominos.
The flaw in Terry's reasoning is that he's only considering things from the perspective of the state 1 dominos. You have to look at it from the perspective of the state 2 dominos, since they are the dominos actually traveling through time.
From their perspective along their timeline, they still originate from the finite set of state 1 dominos. Along their timeline they still have a definite relationship to the dominos in their past and at no time were dominos created or destroyed. So in this sense, even though the rules appear to be broken from the pov of the state 1 dominos, from the pov of state 2 dominos they aren't. They are conserved locally.