Imagine hearing about a play that ran for one night only.
Everything you know about it is second-hand at best. If you’re lucky, you might be able to talk to someone who saw it. If you’re really lucky, they’ll even be telling the truth. More likely, everything that comes to you is of the “I know a guy whose second cousin’s former roomate was in the audience” variety.
With a bit of digging, maybe you can get your hands on some of the props and costumes, though there’s nothing to tell you how they were used. Maybe even a few pages of the script - though as any student of theatre can tell you, what it says in the script and what actually went down on stage are often two very different things.
Now: imagine writing fanfic based on this play you’ve never seen and never will, without so much as a decent plot summary to guide you.
If that sounds reasonable to you, congratulations: you may have what it takes to be an historian.