More Detail Than Anderson

Because Audrey Niffenegger focuses on the time travel aspect of Henry's and Clare's relationship, she goes into more detail than Poul Anderson or any other time travel author thinks of. Thus, young Clare notices that, when Henry comes from 1988, 1989 or 2000, he is upset or freaked but he is ok in 2001. He tells her not to date one of her drawings of him because it is not dated in the future but she dates it. When he returns to his "present," that drawing is not where it should be on the wall. It has fallen down behind some furniture. When retrieved, it is not dated and Henry notices that the bottom of the sheet has been trimmed off. Clare had got worried and trimmed it off.

"...why does it feel as if something impossible almost happened? Why do I feel so relieved?" 

-The Time Traveller's Wife, p. 106.

Some sequences of events are consistent and can happen whereas others are not and cannot. There is a psychological explanation for what happens with the drawing. If Clare were the sort of person who, having been told not to date the drawing, would date it and would not trim off the date, then Henry would have seen the drawing dated in the future and would not have told Clare not to date it so she would have dated it and Henry would have seen it dated. Clare not trimming the date off and Henry seeing the drawing undated is an impossible sequence of events which cannot and therefore does not happen. Jack Havig might notice such minutiae but mostly his attention is focussed on the bigger picture.