In 17-32, the corners traditionally set one bar to the person you just passed, then one bar to the next person to pass. In a variant for [19-24] 1c turns BH in PdB.
3C Chain Progression was earlier known as Chaperoned Chain Progression
note: For [25-28] the original texts say no hands, and pass; in the Book 23 version hands are often held, steps are very small