Scott 91 or Scott 85F based on data shown?
Photo of stamp on cover:
Both are rare, if you think you have one send it in for certification. 98 is more likely
@bigmountainlion Which authentication service would you personally trust and use?
These are the major ones, I have bought some expertized stamps, but never sent any stamps myself. https://www.linns.com/news/us-stamps-postal-history/the-big-four-expertizing-groups-in-the-united-states. APS and PF are major stamp organizations.