https://crowd.loc.gov/campaigns/letters-to-lincoln/1830-1839...
There's a lot of academic research (see e.g. https://transkribus.eu/Transkribus/) but that's in progress rather than done.
https://crowd.loc.gov/campaigns/civil-war-soldiers-disabled-...
A left-handed penmanship contest for soldiers who lost their right arms and were relearning to write. Some of them are remarkably good considering, but some are barely legible.
https://crowd.loc.gov/campaigns/letters-to-lincoln/1830-1839...
There's a lot of academic research (see e.g. https://transkribus.eu/Transkribus/) but that's in progress rather than done.