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I'm not a structural engineer, despite the name of my employer.

However, I agree with you about the enormous power of thermal movements to crack masonry.

In this case, the presence of horizontal (I think) cracks in the stone on the northern elevation in a northern part of North America suggests to me that thermal movements might not be a big part of the problem.

However, this just reminded me of something else.  What is the backup structure?  If it is continuous brickwork, then perhaps the brickwork has grown slightly (some bricks are susceptible to long term moisture related expansion).  However, this would tend to express the cracks earlier rather than later, as the rate of expansion tapers off with time.

Cracks are durned difficult little critters to work out sometime, and you almost always need a big picture.

david