I have downloaded the Posts.7z dataset from here. I have not been able to find a README file, so I go by intuition regarding the content of the file.
To my understanding, a single line of the file is a post on Stack Overflow. Each line/post is an OrderedDict with keys containing, for example, the text of the post (whatever it is a question or an answer).
I have not been able to find/identify the key containing the ID of the user who originally posted. I can only see the key containing the ID of the user who owns the post and of the user who lastly modified it.
How can I get the ID of the user who originally posted a Stack Overflow post?
BONUS: How is it possible that two posts can have different IDs of the user who owns it, but the same DisplayName of the user who owns the post?