There is a lot of nuance to session playing. The most basic is the hourly union rate. You don't automatically sign away all your rights, but in most cases the contract you sign when you take the session will say you get the rate, or "paid to perform for hire", meaning you only get paid to lay it down. Now, typically, that means the piece is already completely written, has a pre-arranged bass part or darn close to it. I get paid to play your notes.
When you look at some of the session work they were doing back then, and the fact that like in Nashville the numbering scheme opens that up for a little interpretation. If you give me just a chord chart and ask me to come up with the bassline, I'm going to ask for a very small royalty on the publishing, because although I am not the writer or given a co-writer credit, I still am materially writing or creating something that didn't exist before. That royalty may be a crumb, but I usually ask and will get it.
The example of Carol Kaye being a session player for Brian Wilson is a good example. Brian wrote out all the parts he thought should be. He wrote out the bass charts. He would give Carol a little leeway on how the line was played, but he basically wrote it. Same for the one she talks about a lot, "The Beat Goes On". Now, she was a session player, and the line she came up with was different then what was charted. So it becomes gray legally, although back then everyone was making decent money and they didn't fret over it much.
I have been involved in legal actions like Flea and others over writing credits for a lot of similar reasons. I had a contract once that specifically said that I get one half of one percent of the original writer's publishing (he had co-publishing, so that for me was one half of one percent of 50%) or a co-writing credit. She decided to not give me the co-writing credit, and when she sold a few CD's I came knocking. Six months of attorneys writing letters, telling me I was not material to the song. I had a contract that said I was, didn't matter if all I did was pedal eighth notes. The song was picked up for a local car dealer ad campaign, and interestingly most of what they used was my bass in the background and the owner speaking over it. My work, my pay.
I'll say it again, yes, Carol could have maybe done some finances differently and that would have assisted her situation. But I have seen her DVD on YouTube and a couple of other websites, and she did not authorize that. A friend of mine asked his kid to see if he could pull it using bit torrent, and he was able to. All this is clearly a violation, and it does effect her pocket book.
Lets assume you were 75 years old, and for the past five years you averaged $50K in book and DVD sales. Now, lets say you anticipate it will drop over the next five years, maybe 10% a year. You set up your finances to anticipate that, and you can adjust to some fluctuation. But now, lets say it drops 60%, but you find out that there were 20,000 P2P and bit torrent shares. I'd say that these illegal downloads or shares definitely could put you on the breadline, quickly.
I brought up the point originally about the rap "fartish", as someonce said, because of the attitude, not the specific nuance of using a direct bassline or song.
I'm surprised, right now there are a bunch of people "occupying" Wall Street supposedly against corporate greed and lack of jobs. Ask these same people if they should have to pay for music or if they do and I bet you most would say no.
My point is, if you are illegally sharing these things, or using them illegally and know you are using them illegally, why would you care who makes money? Obviously, you don't need money, because you take everything for free.
I have copyrights on several songs that are me singing over bass. I then will copyright some of the same songs in full performance version. Costs me the extra $35, but I don't wind up in this fight about who owns the bassline.
As for basslines that are the same as older works, if its now public domain its okay, but you shouldn't be able to specifically claim a royalty for it. Now, if it is part of a larger work and you get some master recording royalty, different story.
Either way, I am enthused that everyone is assisting Carol by buying her stuff and leading others to do it. I hope we can help her out a bit, and when the time comes, which I hope it won't, I hope everyone here that needs our help we can do something.