Everard's Importance

Manson Everard was recruited into the Time Patrol in 1955. We last see him in the twentieth century in 1990. Yet, with his base in that thirty five year period, he deals with several cases that could have resulted in history being changed out of recognition. In fact, on two occasions, history is changed out of recognition and has to be changed back.

Everard has "'...become one of the more important agents operating within the past three millennia.'"
-Poul Anderson, The Shield Of Time (New York, 1991), p. 263.

But the Patrol guards a million years so three millennia are very little. If so many potential, and in two cases actual, catastrophes can be encountered by one agent in such a short span of his career, then is reality really as stable as the Patrol claims? We are told that time travel is allowed because the time lines usually adjust to any changes made by time travelers and that overcoming temporal inertia in order to divert the course of history is hard work but, in the light of Everard's experience, is this true? Or is Everard unusual for some reason?