The author does not makes up new things, as a previous reviewer commented, almost all information given is traceable, with maybe a few details that JK left open filled. The only thing made up is the mc supposition of how modern magic originated and mc's innovative training and reasoning, but even then the *nature* of magic itself is spot on with JK's vision, from what I've seen.
If you expect a fanfiction to keep all the plot of the original and not add anything new then you're in the wrong place friend.