Hello Larry:
I do understand you question and have reviewed this myself several times.
Most all the manufacturer of modern day medical gas manifolds are suppling this type source valve.
1) full port.
2) three piece
3) clean for oxygen use.
4) with a brazed connect on patient side and a threaded connections on the manifold side.
This in my opinion is compliant with NFPA 99 Codes.
The requirement for this source valve is based on the pipeline distribution system.
Which starts at the source valve and continues to the patient outlets and inlets.
So, the upstream side of the source valve can have threaded connections.
Happy Holidays To All