[z2]

Naive question: could this have been survivorship bias? Could certain ones not have been written down or kept with the others?

[nestorD]

I doubt it. The I Ching does not really have bad / low interest hexagrams. Also historians who studied the topic seem pretty sure that the yarrow stalk method is a recent introduction (by I Ching standards, we are talking about a bronze age divination tool...).