This post is a little dated, however, I stumbled across it this morning and figured I'd reply.
I went back and reread this section of the book, and also some other literature I have on hand from some training I've done with Peter. At first glance, it did seem a little contradictory. However, after a second look, it makes sense. Where Peter is initially talking about late lactation milk having high solids, this is in reference to late lactation milk from a seasonal dairying operation. In some of his other writings, he includes several graphs that clearly illustrate the increase in milk solids later in lactation in seasonal milking operations. This is partially tied to the diet of the animal, including decrease in water consumption, change in moisture content of the feed (especially if hay is being fed), as well as the stage of lactation of the animal. One thing to note, is that on page 211-212, he notes that this is in reference to milk that is "of good quality and not altered by late-lactation effects that would cause problems in making cheese". Here he even references the other section.
The section that discusses late lactation milk as being problematic, it doesn't state that all late lactation milk has this problem. In fact, he says it's often tied to seasonal grazing operations, when feed available in pasture becomes sparse late in the season. So poor quality nutrition is a component in creating poor quality, late lactation milk. Furthermore, he states that if a good-quality diet and good udder health are maintained, the cheese making season can go for a full lactation. If that's the case, and the noted seasonal adjustments are made as you outlined in your post, late lactation milk can actually be beneficial for the cheese maker due to higher solids and increased yield.
How do you know if your milk is problematic in late lactation? I'd say as a cheese maker, you've got two tools to work with. First of all, you can test the milk. Problematic late lactation milk has a high pH and high SCC. For cow's this means >6.8pH and >500,000 SCC. Second of all, and this is probably your first indication, would be how the milk performs in the make process. Slow starter activity, long curdling times & soft curd formation, and poor whey drainage would all be indicative.
Hopefully that helps... Obviously, a little bit late! That said, this time of year it could be a relevant topic for lots of people, depending on location. I know it's something I'm keeping an eye out for at the creamery with each of my makes.
Happy New Year!