Mapping to ‘code’ datatype elements

So we’re providing a FHIR interface to our existing data repository. The repository is populated from v2 messages (among other sources).

One issue we’ve come across is when mapping to a code datatype with a fixed value set and you have a code that is not in the fixed set (Something I assume will be quite common). The ‘official’ way to manage this is to find the closest match from the fixed set and use that, and then create an extension to put the more specific code. The thinking is that anyone compliant with the specification will understand the fixed set value, and it shouldn’t matter if they don’t understand the more detailed one (you’d use modifierExtension if it did matter).

But what do you do when you can’t tell what the most appropriate mapping is? Suppose your system collects data from other sources and you don’t have control over what coding those sources use? (Now, I know you should, but this doesn’t always happen). And there are situations out there where only text is provided…

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