Are they sketches loosely related or are they part of a grand design? : Let the Great World Spin

Not sure exactly the direction Colum McCannn is heading as about half-way through "Let the Great World Spin" he includes a section, all in short first-person diary-like entries (set in 1974, this is well before the era of blogs) of the Bronx prostitute who was arrested on the day of the book's events (day that Petit crossed the WTC towers on a tightrope, day that Nixon resigned?). He keeps swinging back to a set of central characters - the Corrigan brothers, one of whom dies in a car accident and the other seemingly stays on in NYC, and their relation with the prostitutes in the Bronx whom both brothers befriend. Not sure really why this is so important to McCann and his story or how they tie to the man on the wire except that the days roughly (or exactly) coincide. Also McCann has for the moment lost sight of the mothers whose sons died in Vietnam, particularly the East Side mother, Clair. If the Clair chapter echoed Mrs. Dallowy, this prostitute's diary, oddly, echoes Ulysses - a bit of a Nighttown element to it. Also, McCann shows his facility at a variety of narrative styles and voices, from more reserved and elegant first-person to this section, which is rough, jottings, street talk. He's slowly assembling something with great skill, but I'm not sure yet whether I see the big picture. Are these a number of sketches loosely related or is McCann working toward a single, unifying theme? I have faith that he is. He is very skilled and each of these sections is compelling and easy to read, and I think each would stand up well in isolation - but McCann goes to such trouble to set them on a particular day against the background of the tightrope walker that I have to think there's a purpose other than simply building a link of temporal coincidence.