I know a guy who has made and/or sold between 1000-2000 primitive and modern traditional bows. I asked. He said that as far as he knows none of them has ever broke. The one's that break, break during tillering.
My personal experience is that the "older" bows are more likely to break, especially the laminated bows, to the point that I refuse to pull one when I recognize it as 60's or early.