Seems like moisture content might have something to do with it. Remember that 99 that cracked sitting in my safe? I bought it from Missouri and unless I just flat out missed seeing it, two weeks later I took it out and it was plainly cracked.
Just guessin'.
Lack of moisture is definitely a factor, solid wood acoustic guitars with a top as thin as 3/16 have been known to crack if not kept in a humidity controlled environment, especially in the winter when humidity is low.
But if that's a major cause, wouldn't you find more 99's with tang cracks in northern climates?
I live in canada and only one of my 99's has a small crack.
Just an observation.
