What would I need to do to get the stamp "on the record" and see if others exist?
Tough question Nells,
my personal route is to mount, label and forget it.
During your collecting, if happenstance occurs, you may see it questioned in your travels.
from time to time using the Sc#
Ask at your local Stamp Club.
Enquire as to US EFO catalogues if they exist?
You may be amazed at what some collectors catalogue.
Here's an Australian example: