when does private mean private?

Let me know if I have the "private" theory correct.

Only a contact can be marked "private."

Once marked "private," all the "private" contact's emails are still visible via show activity button on the lead>prospect>customer> form to which the "private" contact is attached so it is not really "private" unless it is disconnected the from lead>prospect>customer form.

As long as a "private" contact is independent, all its messages are "private?"

And then the files attached to the "private" contact are never really "private" because they can be found in a global search by their name. So if I make a ducument for a "private" contact that I want to keep "private" I need to give it an obscure name. Or will these obscurely named documents still be searchable in a dated search?? So the only truly "private" stuff is messages and activities on a "private" contact and nothing attached is truly "private?"