If you shoot film, and later you scan it, especially into formats like DNG, you end up with a file that is poor in metadata. Your scanner software (like VueScan) knows about the scanner perhaps a Plustek 8100 and the scan settings, but it has no idea what camera or lens took the original photo.
This leaves a gap in your digital library.

To fix this, I use ExifTool to add the relevant EXIF tags to the scanned files.

Here is a single command I use to batch-process a directory of DNGs to embed all the correct metadata for a specific camera and lens combination.

exiftool -overwrite_original -r -ext dng \
-Make="Leica Camera AG" \
-Model="LEICA M6" \
-SerialNumber="<camera serial number>" \
-LensMake="Leica Camera AG" \
-LensModel="Summicron-M 1:2/35 ASPH." \
-LensID="Summicron-M 1:2/35 ASPH." -LensInfo="35mm f/2" \
-FocalLength="35.0 mm" \
-Artist="GIOELE MARTELLI" \
-ProfileName="LEICA M6" \
.

-overwrite_original is an important flag. By default, ExifTool creates a backup copy of your original file (e.g., file.dng_original) before writing changes. This flag prevents that, modifying the file in-place.
This is a destructive action. I recommend running the command on copies of your files first until you are confident in the results.

The above command is a "master template". I keep a separate script with variations of this command for my other common combinations.

It's a simple, one-time step per batch of scans that makes my digital archive infinitely more organized and searchable.