Tacitus Two

Manse Everard is first informed of causality violations that have no human cause in The Shield Of Time, Part Five. Despite this, he had referred to probability-waves changing their rhythm in "The Year of the Ransom" and to a reality that can at any instant cease to be in "Star of the Sea." This second story was written after The Shield Of Time but is set earlier than it in terms of Everard's duration sense.

How can we account for the Tacitus Two text in "Star of the Sea"? This text exists in the Time Patrol timeline but reads as if it had been written in an alternative timeline. I have proposed an explanation (see here) (scroll down) but what does Anderson's text imply?

"'An object uncaused, formed out of nothing for no reason.'"
-Poul Anderson, "Star of the Sea" IN Anderson, Time Patrol (Riverdale, NY, 2010), pp. 467-640 AT 20, p. 631.

In quantum mechanics, pairs of matter and anti-matter particles appear in, or emerge from, the energy-filled vacuum. Temporal anomalies are like quantum events scaled up to the human level. So did Tacitus Two just appear on a shelf in a second century A.D. Roman library? This account is logically possible and also avoids reference to a time journey in and out of a potential timeline so which account do you prefer?