my guess is 10 is low, 1000 is high....
I personally know of many collectors sitting on incredible collections, that have never seen the public light of day (non cgc'd, etc)....and if I know of many, I am sure many know of many that I wouldn't...so, they are out there in some number, and we will continue to see them materialize...at what rate, that is the truly unanswerable question (thumbs u
The age of the collector might be a factor. The original owners are beginning to die off, but maybe it will be when the generation after begind to go...say, a generation from now, there will be a fresh explosion! Wild guesswork of course - you'd know best what the average collector age might be!