I am very familiar with that book.
The graph evolved over time - you can imagine when it only had one or three years of data -less cluttered and dense.
I don't use or maintain it anymore as I started using GPS tracking app in April of 2014.
I also think it is OK with the data smeared like it is - being able to see more detail is not needed, it is the trends that show up OK with the smear. But I totally agree there is quite a bit of room for improvement.
The route is all flat. One can see in May-2014 my repeated efforts to get KOM on a 1/3mi segment with that cluster of top speeds.