Good information to have on hand.
A long time tire guy I know said to me, as long as the cracks aren't deep enough to get into the belt area, you are okay. It often can be a tough judgement call as to how deep is too deep?
Recently I took the step of replacing my 5 year old cracked TV tires, for peace of mind. They had been showing cracks for the last 10,000 miles, and slowing getting worse. It's like the guy who jumps out of a 15 story building......as he falls past the third floor, people hear him say....so far so good!
It would be nice if there were a way to measure something to help make the judgement call as to how deep are those cracks?