Yes, but if the information is worth writing down and preserving, one has to balance risks of dissemination with risks of the info being lost.
I think we must also take into account how the journals were handed down. Whether with in a family, which would mean Merlin is Harry's great,great,great, grand something... Yikes, just what would that mean?
Or more likely handed down from master to the most worthy and trusted apprentice, it would not be done willy nilly. You can bet that Merlin did build in safe guards so
the information would not go anywhere except to the person it was intended to go to. It might be as simple as the language it is written in. We are all debating what language it is written in, what if it is all in a code? Simply put, the abilty to read them is inherited along with the journal. That way no one else could ever read them..