I think what has been said about these couple of episodes in private hands (not a huge amount, just a couple) are that they've been known to be in private hands for awhile, and these particular people have no intention of returning them to the BBC, so definitely don't get your hopes up.
There had been rumours and/or speculation for years that a few episodes could have been privately held if, for no other reason, for certain SuperFans to have something no-one else has and somehow feel superior.
That, or they're holding them for a king's ransom that the BBC are unwilling to pay.