MOST STUDIOS will sign you to an agreement which says this is YOUR work and you are allowing them to use it.
This is not factually accurate. When the studios buy your work, they are also buying the copyright. You no longer own it in any way. Unlike a play--which a playwright licenses the work, when you sell a screen play, you are also selling your copyright to it. That's why a studio can fire the original writer and hire someone new, that's why when someone new is hired, they don't own the script.
Working for a studio is all work for hire.
Roddenberry may have created Star Trek, but, he sold his ownership of it. The Studio decided how they were going to use it. That's why it was possible to totally sideline him after the financial failure of TMP.
It's the very reason why there CAN be a union, and why Roddenberry gets credit and residuals. Because writers don't own their copyrights.
Copyright does not magically begin at the moment of creation, it begins at the moment of documentation.
This, too, is factually incorrect.
From the US Gov's copyright office:
When is my work protected?
Your work is under copyright protection the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device.
In other words, once you have finished your novel, your painting, your dance, your play, your screenplay, it is copyrighted.
Also of note, and from the same page...
Do I have to register with your office to be protected?
No. In general, registration is voluntary. Copyright exists from the moment the work is created. You will have to register, however, if you wish to bring a lawsuit for infringement of a U.S. work.
I've asked this question from the very beginning without an answer. If I am no longer able to document the work as mine how do I legally turn it into the studio as legally mine?
Simple answer: your name is on it. You can even put the little (c) thing. But, if your name is on it, they assume you didn't steal it.
You can also register a script with the WGA, you don't have to be a member to do so.
You can also register it with the Copyright office.
But, again, all of that is unnecessary.
So let us for a minute go with the premise that nothing I create belongs to me
Your premise is coming from the flawed basis though. What you create is yours. It gets muddy, obviously, if you are creating something based on something you don't own and isn't in the public domain. But, you know that going in. If you are creating fan films then, really, go in with open eyes: you don't own it, you are playing in someone else's sandbox and they can tell you no.
and could be picked up by a licensed franchise writer for their use.
That I don't know is true. I haven't heard of that happening. In some ways, I don't know of a writer who would be all that excited about lifting someone else's story.
But, then, again, you are playing in someone else's sandbox with THEIR toys... you shouldn't be surprised when they are taken away.
If true why would I or any other freelance writer wish to create anything of any value in the first place? (feels like I'm in a holding pattern)
Well, if you are trying to create value in fan films, you are, from my perspective, wasting your time and creative energy. if you want to create something of value, put it towards something that you would own lock stock and barrel, so you can make it or sell it to someone for money or license it.
I get the idea of it being fun to make a Star Trek film, but, all of this time and energy devoted to something that isn't yours... I, as a writer, don't get at all. I don't know why someone would spend years and years playing with someone else's toys and not go make your own. Then it is YOURS.