That's correct, the hot core used to be a gilding jacket cup with a flux on the inside, and lead injected, but I've also read that they put fluxed cores in and ran the things through an oven to melt the cores. I don't buy the second part.
The new ones, the deep curl, were just plated bullets, no different than the gold dot. Properly formed cores were tumble plated. Internal skiving could be done by ridges on the core. after the cores were plated, they bullets would be run through several swaging operations to perfect profile and set up expansion characteristics, just like they do with gold dots.
munitions makers the world over are still kicking themselves that they came to the plated bullet game so late. Plated bullets date back to the power locked by remington, back past the sixties. We could have had gold dot pistol bullets back in the seventies. This whole thing could have happened in the eighties. I can pretty much guarantee that it costs a whole lot less, but R&D and startup would have been expensive. Operations would have been a piece of cake. A rifle bullet requires over a half dozen drawing and cupping procedures, then other steps related to jacket forming. With a plated bullet, you swage a core with great precision, plate until thickness of jacket is attained, then toss the slug into the machinery to form it.
There is a reason that a plated pistol bullet costs so little. I wonder if a plated rifle bullet like the fusion costs less than half of what a premium drawn and cupped bullet to manufacture.