Do you now, or have you ever, thought that a "Co-PI" was an official designation on an NIH grant?
Where did you come by this notion, if you have?
How recently have you had colleagues describe this as a real thing (and not as a confusion for the Multi-PI)?
Are there other major or minor funding agencies you are aware of that use "Co-PI" in some formal way?
Is it the same as NIH's Multi-PI or more like the "co-I, but better" implied by the old, inaccurate use with respect to NIH grants?