I was being facetious but am now extremely curious about large portion of the knowledge obtained by subject matter experts in any given field has never been published - this is not only strange to me in the small but you are claiming that this is large portion so I am wondering if you have any example(s) to share?

Ah, sorry I missed that.

Academics, whose entire careers are based on publishing knowledge, only publish a fraction of their total knowledge obtained over their career. Estimates are that only 10-20% of all knowledge is explicit.