Assuming there are no other numbers in the directory path, you could use
exiftool "-AllDates<$Directory 00:00:00" /path/to/files
That would set the EXIF timestamps to midnight on the date in the filepath.
If there are other numbers in the directory path, then a complex command would have to be used. Assuming the date is exactly as you posted
There's no subset of metadata that is specialized for scanned images, so you'll have to use standard tags, possibly re-purposing some for your own use.
Trying to figure out what tags to use based upon what exiftool can edit isn't the best way to go about it, as exiftool can edit thousands of obscure tags that don't get much everyday usage. You're best bet ...
I used XnView for batch renaming.
XnView is a free Image Viewer to easily open and edit your photo file.
You can try to use photo`s Modified date or EXIF data (if it exists) in renaming rules.
Here my settings for renaming: