The main idea here that we strongly need to avoid subjective reasoning.
Scars is a very good example. For me Scars are conditions. And we can argue with @m-khitrun and both of us will find valid arguments based on our clinical knowledge.
The problem occurs when I need patients with particular symptoms or disorders having these symptoms. Then I always need to look in both tables.
The proposal is to put everything in Condition with some exceptions.
If we’ll get false positive Conditions like Item held as scanned document or findings of demografic history , nobody cares.
The problem will only exist when you need to store values.
In this case I would list all concepts of this kind (allergic reaction to, requires vaccination of, etc. - we can discuss this list), so users can see it instead of guessing.
And use similar approach with potential measurements, where you already started postcoordination. I’m not sure what to do with Obesity example, as it has values as intervals, such as Child body mass index 92nd-97th centile.
So there will be a simple rule:
if it’s symptom or state, look in Condition domain
if it looks like postcoordination, check with the list of postcoordinated concepts and look in Measurement or Observation.