I still question the assumption that they were trying to put anything in orbit. The question is did the stages separate properly? Because mastering multistage rocketry is the key for producing long range ballistic missiles.
I'm with you. I doubt this was ever intended as a satellite launch attempt. I think that was a (thin) smokescreen to appease the international community.
I think they were testing their revised first stage, working on their staging, testing their (new?) third stage, and probably checking out a re-entry vehicle design.
As you say, staging is a critical technique. They've also had problems with their first stage before. I think the third stage was new on this shot. Finally, you can test RVs on shorter range missiles, but they don't come down with the same kinetic energy - they really needed to loft one completely out of the atmosphere and re-enter at a realistic angle and velocity.
I think their "satellite" launch was a "failure" but their test (assuming they were able to collect their data) was a success. It would appear from news reports that the third stage did burn. Not sure if they got RV separation or not, nor what kind of range they were able to achieve...