Ready.
On copycat's page 144, there is only the "Fig.6.3." that shows the internals of the "putbuf" as referred to, in "Fig.6.2." (on page 143). This figure corresponds to the "Fig.8." in copycat83.
The place p4 has double-existence. When shuffling pages to trace what the example means, finding it only once, does not suffice. As a result, a reader must exhaustively read every label, next to each element, when referring to any figure, to find out what that element does. It is similar to find all your photos, in a pile, without any idea about how many of them, the photographer had printed. Each time, with every pile, when looking for something.
copycat82 is exactly false, when p4 points to both the "full(BUF)?" and to the "WP=0" rectangles. The latter rectangle, follows the former, but it also requires a token-existence in p4. This is impossible. As such, the "Fig.6.2." could have never been verified. It is exactly faulty.