Infiltration

In Poul Anderson's There Will Be Time (New York, 1973), there are four different reasons why time travelers go to Jerusalem on the original Good Friday:

"...Coenraad van Leuven, a man-at-arms from thirteenth-century Brabant..." (p. 62), goes to witness, and even tries to prevent, the Crucifixion;

Jack Havig hopes to meet fellow time travelers;

the Eyrie hopes to recruit time travelers;

the seventeenth century Orthodox monk, Boris, goes to infiltrate the Eyrie for Havig's group.

Thus, Havig's presence in Jerusalem is the beginning of his interactions with other time travelers whereas Boris' presence represents a much later stage of those same interactions, when Havig has left the Eyrie and founded a rival group. Boris, "...who spoke only Croatian (?)..." (ibid.) keeps quiet although he must know a lot and indeed already knows Jack.

There is a third stage. When Havig's group has defeated the Eyrie, a few of the Eyrie's men escape but are probably demoralized and will also realize that, if they try to warn the Eyrie at an earlier date, then they will stopped by Havig's agents, like Boris, planted in the Eyrie throughout its existence.

Thus, within a single timeline, there are successive levels of sophistication of Havig's activities and understanding. Another example is provided when Havig and Leonce flee back into the past on their first sight of human beings accompanied by extraterrestrials but later initiate the interstellar travel that leads to human contact with extraterrestrials.