Your description is largely accurate. In the process of making these beads they were removed from the molds. twisted, and replaced. Offhand, I cannot think of any versions that have pre-made inserts: though other types of powderglass beads may have them. Zagba are distinct from older powderglass beads, but were most-likely inspired by them. Modern (post 1960s) beads diverged considerably, though new traditional-looking beads might be made at any time.

I took a hands-on class to experience powderglass beadmaking, in 2005. This is a photo of me charging a mold. Followed by the actual beads I made. I cannot say I learned anything I didn't already know about powderglass beadmaking. But it was rewarding, to have experienced it.

JDA.