Phil Palmer talks about this in his book, that there is a grey line between contribution and composition, and from the sideman's part, is a big risk. He says that when you are recording and your part is really more a composition of you own than a contribution, you have two choices:
1/ Ask inmediatly for the credit, if you let it go for a day or two, is lost battle
2/ Don't say a thing, because if you ask for a credit and you deserve it, you might get it, but that artist won't call you anymore, and probably would spread the word and you would be in danger of no loosing jobs
He says in the book he always opted for not saying a thing, and keep getting jobs. He mentions some sessions where he wrote the main riffs for the songs, or creating a great and catchy solo that made the song famous or reconizable, but he chose to be proud of his work, and keep working, than have a credit and not work anymore.
Looks tricky, and Bobby Valentino took a big risk with this. Other artists that might hire him maybe would choose another one just in case and not take the risk he might ask for credit.
It's a very interesting discussion! History shows that songwriting credits are a complete mess sometimes and an ever-changing thing. I always found it too confusing with Lennon/McCartney vs. McCartney/Lennon thing, they had songs clearly written by one, credited to both, etc., I don't think that Mike Love deserved some of the writing credits for The Beach Boys songs and so on. I don't think that coming up with a couple of words to a finished song or an instrumental line is enough to earn credit.
I think if you compose an integral part of the song, or the main riff, or all the lyrics, then it deserves credit. But for a lot of stuff, I don't know... Would "Rüdiger" be the same without an acoustic guitar intro? I don't think so, but the song would be amazing even without it. Can the idea change the song's feel completely? Sure, but that would not change the song. Allegedly, Ed Bicknell suggested the unique rhythm drums part for "Your Latest Trick", which arguably made the whole song so iconic. But should he earn writing credit for that? I don't think so...
A lot of times you have a direct influence on the songs, like Ringo Starr coining the term "a hard day's night" or Paul McCartney's driver saying "eight days a week" that would result in a song. But this idea on its own would certainly not write the song, it's just an idea floating in the air. The idea is nothing without a result.
How does it translate to Alan’s situation? I think without MK, he won’t be on Montserrat recording an album and without Mark writing the song Money For Nothing, he won’t be suggesting to put Sting’s melody in it. I think Mark did the most work there and any idea would be nothing compared to his contributions. Like, it’s not even comparable. Who knows, maybe he would eventually come up with an even better solution. Like the iconic Brothers In Arms intro lick!
I think it's a generally stupid idea to go fishing for credits if you're a session musician. If the artist you work with is not dumb, I don’t think he would argue about giving you the credit. Most of the time it’s just not worth it! And a session musician may come across as a selfish, greedy a-hole and hence get fewer job later on. If that’s polite and arguments are strong, it's not a problem. In Bobby’s case, arguments were strong, but only in court! Just don’t leave this decision for a court is what I'd say.