ICD-10 codes: required to go to most-granular level?

Question

Given the example ICD-10 codes below, will a diagnosis code ever not be the most-granular option within a given classification? For example, could a patient's code be left at I21.0 and not taken to the deepest level (e.g. I21.01, I21.02, or I21.09), or is it required that the diagnosis code "tree" for a given diagnosis be "exhausted?"

I21 ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction
  I21.0 ST elevation (STEMI) myocardial infarction of anterior wall
    I21.01 is a specific ICD-10-CM diagnosis code I21.01 ST elevation (STEMI) myocardial infarction involving left main coronary artery
    I21.02 is a specific ICD-10-CM diagnosis code I21.02 ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery
    I21.09 is a specific ICD-10-CM diagnosis code I21.09 ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall
  I21.1 ST elevation (STEMI) myocardial infarction of inferior wall

Answer 1

It does not have to exhausted.

The best way would be to point to coder's guideline.

Instead, I will use a data method to prove it. To prove it via data, you can analyze data from Columbia Open Health Data (from Columbia U in NYC) and look for broad terms and you would see that they have counts that are greater than sum of the most granular terms.

COHD data comes as ICD and gets mapped to SNOMED CT terms. But the issue of parent vs. detailed child is preserved. (even after the mapping)

data reference: https://www.nature.com/articles/sdata2018273 data API: http://smart-api.info/ui/9fbeaeabd19b334fa0f1932aa111bf35

API output for a single term. You must traverse SNOMED CT hiearchy for the related terms.