in Mail, how is a person's name associated with an address?

I have a situation where email addresses for a position (treasuerer@example.com) are moved from one person to another as things change.

Problem is, on an incoming message that's listed as coming from e.g., Bob<treasuerer@example.com> when the responsibility is moved to Pat, so I'd like that to show up as Pat<treasuerer@example.com>

I thought this came from the Previous Recipients list, so cleared out the corresponding entries there, but there was no effect on the incoming messages.

Can someone tell me how to un-do these assignments, and/or how to re-establish new assignments of name to address?

Thanks!