Should one expect to see individual NPIs under "institutional" class

[lisuhui666]

The schema's definition of billing_class is below:
Allowed values: "professional", "institutional"

I had assumed that that billing class distinguishes facility vs. professional claims (UB04 vs CMS-1500 forms). Under that assumption, I’d expect to see only organizational NPIs under the "institutional" class because rates represent facility fees. However, I see in Aetna, United, and BCBS files that there are more individual NPIs than organizational NPIs under the “institutional” class. Can someone help me interpret these rates? If the rates apply to individual physicians, should them be reported under the "professional" billing class with appropriate service codes?