It seems the Metadata model won't give you this piece of information for every object, albeit only for a few of them
like Reports, Jobs etc. which keep an association with a Person object as Author. Even with them, I am not sure
the "authorship" keeps track of the last Person, perhaps only the one who has created the object.
This model might not have beed designed primarily to be used like a versioning repository like SVN, GitHub etc
I am not a regular user of the OMI, so don't hesitate to correct me if I'm wrong .