I am a freelance writer. Not only do I thoroughly understand the nature of work for hire, I have also accepted many assignments on a "project" basis. That means I got paid a bulk fee when the project was completed. If my writing was absolutely dazzling, I might get the first draft approved (not a regular occurrence, but it has happened). If not, I kept writing until the project was accepted as satisfactory by my employer. Sometimes fourth and fifth drafts (again, rare, but it has happened).

Same risk that Kirby took having his pages rejected.

He worked under this system for how many years? And worked under a similar system at DC, Harvey, and how many other publishers? He had watched Captain America continue to make money for Martin Goodman all the way through World War II and into the 1950's. Never a lawsuit. No claims of ownership.

To argue that Jack was ignorant of his employment conditions is simply not credible.