I have been wondering about that.
I've never heard of a captured converter pen that having problems with ink getting trapped in the converter. I assume that pens with a captured converter use something higher quality and more durable than a standard converter.
But my guess is producers just buy these units standard from Schmidt.
If you go to the Schmidt webside you can download their catalogue, with many complete sets. As a penmaker you just have to make a nice coat for these systems and you are ready to go.
But a pen like the CS Winston can be had with a standard C/C. So I guess the trapped converter is just standard, with just a system to operate the screw from behing instead of opening the pen.
Tha large Stipula converter is a whole different matter. This is a metal affair if I remember well. Perhaps WIMG can shed some light on that.