To clarify some points about intellectual property (IANAL btw):
There are a few forms of IP relevant here.
1) Copyright
2) Patent
3) Trademark
4) Trade Secret
What most of you are talking about isn't copyright, it's #4, Trade Secret.
Mixing is about a PROCESS of taking given input and generating given output. This could be protected by Patent or Trade Secret protections. Patents would be hard to obtain here; you might invent something like putting an oscillator on a sidechain to make that Belgian dance throb effect and patent it, but most mixing processes would be invalidated by the "prior art" clause.
Still, you can argue that your specific mixing technique is a trade secret and that is what you are in fact saying. Copyright has nothing to do with it...you could, I guess, copyright your DAW session files and recall data, but that would be a total waste of time. Trade secrets are what you are arguing, and those are indeed protected even though they obviously aren't registered with the gov't like other IP's.
Trademarks refer to your brand...hiphoppers/R&Bers have recently taken to putting "tags" on their "beats" where they have some sexy or robotic voice say the name of their studio or producer at the start of a song. That would be a trademark and you could argue rights over where those trademarks are placed (i.e. on everything you make and nothing you didn't approve of, etc.).
But back to trade secrets; it's all negotiable, as stated, as to what you will yield or expect from a client. You can, as a mixer, sign a nondisclosure agreement covering your trade secrets, which would prevent what Kenny is worried about but still give the client recall capability of the ITB mix. You could put the recall data into an escrow service. There's tons of things you could do.
But more practically, the general gist to the OP here is that "real mixers" start from scratch (well, usually final edits are nice to have) and so the recall data is usually of little use. However, it's possible that a special effect was achieved at the earlier studio that people want to retain...for instance, a specific Filter Freak setting that is endemic to the production...and in those cases, a print of that effect or recall data is something the client should negotiate for with the earlier mixer.
"I never say no, I only quote a price..."
