Mistakes in 'The Time Traveler's Wife' book?

I’m currently re-reading this book, and enjoying it again, but something is bugging me. In the scene where Henry is talking to Gomez in the restaurant and first tells him about his time-travelling, he says:

(emphasis added)

But when they first meet on September 23, 1977, the chapter heading says “Henry is 36, Clare is 6”. That also ties up with the scene directly afterwards, when Henry returns to his present after the first meeting - it is February 9, 2000. We know Henry was born on June 16, 1963, so he was indeed 36.

Actually, I’ve just noticed another thing:

At their second meeting in the Meadow, six days (in Clare’s time) after their first, on September 29, the chapter heading says “Clare is 6, Henry is 35”, and yet Henry says: “A few minutes ago it was Monday, March 27, 2000.”. So that was after the first meeting in Henry’s timeline too, and Henry would be 36, not 35.

Have I forgotten something later in the book that explains this, or is it just sloppiness?