Causal Loops And Temporal Vortices

When Manson Everard of the Time Patrol investigates the disappearance, in Peru, 1533, of Patrol Specialist Stephen Tamberly, Tamberly's wife, Helen, asks:

"'There'll be a report in the files. Can't you go at once and read it? Or, or skip ahead in time and ask your future self? Why must we go through this?'"
-Poul Anderson, Time Patrol (New York, 2006), p. 670.

We know the answer. If Everard's future self tells him that he failed, then how can Everard try to succeed? Indeed, he would then be trying to change events whereas the Patrol is meant to preserve them - although this is what Everard did in "Brave To Be A King," unless the Patrol instructed its Records Department to lie by saying that Keith Denison never returned from ancient Persia?

Everard replies in part:

"'Causal loops can too easily turn into temporal vortices.'" (p. 671)

Here the concept of a "vortex" is used again without explanation. If a causal loop is the circular causality paradox and if a vortex is the causality violation paradox, then how can the former become the latter? The difference is between me causing my parents to meet and me preventing them from meeting.

However, Everard does elucidate:

"'Just think how our actions would be influenced by what we believed was foreknowledge.'" (ibid.)

If we believe that we will succeed and therefore do not try hard enough, then we will fail. Thus, an attempt to benefit from a causal loop might instead cause a causality violation.