This doesn't account for the stake stinc ninja mined with sock puppets.
The number of accounts mining was high by design, but the number of Devs capable of mining far fewer.
We don't yet know where that ninja mined stake is, nor whether it powers up and witness votes, or keeps dumping.
Thanks for commenting. I don't have all the answers to the questions you pose here, there definitely was a high number of accounts - please see my post today - I think there were circa 155 designated mining accounts, and there is 300k of STEEM still in those accounts....
https://steemit.com/ocd/@cryptocurator/are-these-steemit-inc-ninja-accounts-is-there-an-unfrozen-whale