The Mongol Paradox

NOTE: See the combox for a correction to this post.

We can appreciate the Time Patrol series but still understand the paradoxes differently. What happens in "The Only Game In Town"?

Denison sees Mongols in North America in 1280 A.D. and returns to the twentieth century. I think that, if those Mongols had been going to conquer North America, then Denison would have arrived in the twentieth century of a timeline in which the Mongols had conquered North America. Instead, he arrives in his familiar New York. This means that, in this timeline, someone or something prevented a Mongol conquest. Denison will learn that that someone was himself and Everard. It follows, I think, that, if Everard and he had not set off on their mission to thwart the Mongols, then the first unwelcome consequence would have been the arrival in the twentieth century of the Everard and Denison who had thwarted the Mongols. By failing to embark on the mission, they would unwittingly have duplicated themselves.

Another conceivable consequence would be that...

Leave it there for the moment. I think that:

Everard and Denison are in a timeline where the Mongol conquest was prevented;

but they are still obliged to travel to 1280 to prevent the conquest;

but, if they do not travel to 1280 for this purpose, it must remain the case that they are in a timeline where the conquest was prevented;

therefore, it was prevented by an Everard and a Denison who remembered having traveled then for that purpose and who would, as they saw it, "return" home.