from Dunlop site...I was surprised when I read it too. Worth a look dunlopracing.com/technical-info
How many Heat Cycles can I get out of a tire?
Heat Cycles is not an issue with Dunlop racing tires as it would be with other brands. The more important factor is how much tread is left on the tire. Stable fact: thicker rubber has more grip and develops more heat, thinner rubber has less grip and runs cooler. After each session you have less grip. As the tire wears out, you have less and less grip. It could be slight or it could be large.
Some riders call it heat cycling, but, in actuality, its the rubber getting thinner and thinner. It truly depends on how much the tire is worn out, and your specific demands for grip that determines when the tire is not usable for you.