2c389a02__Specifications___openEHR_wiki__openEHR_equivalent
[0] 3 [Code mnemonic] QS [Rubric] sufficient quantity [Description] The specific quantity is not known, but is known to be non-zero and is not specified because it makes up the bulk of the material.'Add 10mg of ingredient X, 50mg of ingredient Y, and sufficient quantity of water to 100mL.' The null flavor would be used to express the quantity of water. [openEHR equivalent] 
In openEHR, this is not missing data. It just happens to be quantitative data that is expressed in narrative form. Modelled in archetypes by allowing a narrative alternative to a quantity. Fine, but narrative is not the same. There are systems that can figure out how to profitable use QS as a notion. Narrative is much wider.
Null Flavours and Boolean data in openEHR - Specifications - openEHR wiki
openEHR equivalent