15c Lincoln Stamp on cover dated Oct 26, 1868

NateInSav

Scott 91 or Scott 85F based on data shown?

Exhibit A:

Exhibit B:

Exhibit C:

Photo of stamp on cover:

bigmountainlion

Both are rare, if you think you have one send it in for certification. 98 is more likely

NateInSav

@bigmountainlion Which authentication service would you personally trust and use?

bigmountainlion

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.