Extremely Loud and Incredibly Close Lesson Plan

What does Thomas Sr.'s final letter reveal about Oskar's discovery months earlier at the art supply store?

Thomas decided to sculpt his wife after he came back to New York, so he went to the art supply store nearby to find clay. While he was there, he wandered around transfixed by all the markers and pencils, writing his name on every sample sheet he could find. Perceptive readers will realize that it was Thomas Schell Sr.'s name that Oskar saw when he was at the art supply store, not his father's. This solves the mystery of the timeframe, since the sheets were put out after Oskar's father died. This connects to the theme of being "incredibly close" that comes up at...