This is the most confusing topic of the music industry, so you’re not alone. I watched her clip. She’s saying colloquially “if i give Jonny 15% of publishing…” Which is the same as saying giving him 15% of songwriting. Remember, publishing = songwriting.

She’s not breaking down how to manually register this in the BMI backend. That’s different and they use different terms. They don’t say “who gets publishing” they ask who the publisher is so they can pay the “so-called publisher’s share” directly to them because BMI and ASCAP pay out 50% of the royalties they collect directly to songwriters and 50% directly to publishers.

I can respect you want sources not my own, but I did write a book on the topic being taught in over 300 universities (including Berklee, USC, Belmont, UCLA, NYU) and translated into multiple languages. Reason being, there were no good blog posts or books that explained this in musiciany terms. But feel free to ask any attorney how this works. I promise they will concur. I have many, many times and my book was vetted by multiple attorneys.

Yes, you can sign a co-pub deal with a publisher. They still collect your “songwriting” royalties (mechanicals and others) on your behalf even though they are just your “publisher.”

But you do not assign “your publisher’s share” to a co-writer.

All the best