Pursuant to FHIR-40249, for Coding and CodeableConcept we say that they SHOULD contain a value from a preferred value set. I do not believe that this is consistent with our usual meaning of the word SHOULD, where implementers are expected to conform but there are some cases where they need not (see https://build.fhir.org/conformance-rules.html#conflang).

I don't believe that this language reflects the values expressed at the start of the section: "Instances are encouraged to draw from the specified codes for interoperability purposes but are not required to do so to be considered conformant."

Are encouraged is not the same as SHOULD, and further we say - very intentionally - "When an element is bound to a preferred value set, derived profiles MAY bind the element to any value set they choose."