Why the doubt?
I own more than 10 geocoins that I don't intend to circulate. And by comparison, my collection is tiny.
Surely Groundspeak, which has a database of tracking numbers, would know how many trackables there are. I don't know how many numbers end up unused, but as they cost $1.50 each (I think) I don't think there's too many out there.
But if you don't intend to circulate, could you say it's "out there in geocaches"?
It makes you wonder if this also includes lost TB's that have been moved to graveyards?