2c389a02__Specifications___openEHR_wiki__openEHR_equivalent
[0] 3 [Code mnemonic] UNC [Rubric] unencoded [Description] No attempt has been made to encode the information correctly but the raw source information is represented (usually in originalText). [openEHR equivalent] 
Not currently handled explicitly in openEHR. Q: This content can appear at any level of granularity, and usually appears at Composition level. How does HL7 handle this? A: in this case, original text would be a reference to a portion of the text in the composition. It doesn't really add much: the difference between no value, an UNC and an originalText and no value and an originalText is... not much. The vanishingly small use case for this is to distinguish between "I didn't try coding this in snomed" (1st case) and "I tried to code this in snomed, but couldn't" (2nd case) Q2: if one were to use this code wouldn't one then need a place to say more, e.g. which terminology was attempted etc? A2: yes, you do - actually a valueset, really, which may cross terminologies.
Null Flavours and Boolean data in openEHR - Specifications - openEHR wiki
openEHR equivalent