Ok, my lens is in the database, but it is not identified exactly the same way darktable gets it from the image file.
Image file: “Nikon AF-S DX VR Zoom-Nikkor 55-200mm f/4-5.6G IF-ED”
lensfun database: “Nikon AF-S DX Zoom-Nikkor 55-200mm f/4-5.6G ED”
The difference is the “IF-” before the “ED”. I’m not sure what to do to “fix” this. The image files will probably always report the same string. But if I fix it in the database, manually, it will be overlaid every time the database is updated. On my system, the database was last updated on May 16, 2020, so it appears to be a fairly common occurrence.
However, as a one time shot, I edited the lensfun database for that one entry. I restarted darktable, and loaded the lens correction module. It still says it is not found.