What percentage of high grade cards and sets are being held ?

We see many cards for sale via ebay and auction houses, but I was wondering what percentage
of high grade cards and sets are never hitting the auction blocks.
It appears to me that a larger percentage of collections are staying put right now, with
not much movement in any of the 4 major sports. I am only looking at very high grade cards and sets only.
Your thoughts
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Comments
I just asked the owl. He said 38.72%
Did Dan Bassettehound highjack this id ?
Not only are a lot of high grade cards being held, many big collections of rare items are not being graded OR sold.
My collection will never be graded or sold...over 150,000 cards covering every topic, roughly 60% NBA. I didn't even sell duplicates until 2016, and now only on COMC. I don't care about grades too much, but plenty of them are high grade. Most were fresh out of packs...though I will upgrade when available, I generally would rather buy a card I don't have any copies of than buy the same card twice. I don't feel bad about saying how many I've got because I'm slowly scanning them and posting them to my website...still a few years before I finish.