There seems to be some variation in how we record why a request is being made (reason), and how we record "on demand" usage. It isn't clear that this variation is intentional, rather than just separate evolution.

Do all the resources need a boolean asNeeded?

Do they need an asNeededCodableConcept or asNeededFor? Is the meaning the same? Is the intent "as needed when" rather than "as needed for"?

Is it clear about how "as needed" is distinct from the reason for the request?

Suggest using the same structure and definitions across all resources.