LR apparently is structured to meet the needs of professional photographers and unfortunately ignores the needs of amateurs who are scanning in old family photos.
When scanning photos sometimes you only know the year, sometimes the month and year, sometimes the day but rarely the time. In LR you have to edit the capture time one image at a time which can be awhile if you have many images to date. If all the images were scanned the same day LR will change them all to the capture date but assign a time based upon when they were scanned. If they were scanned on different days over the span of a days or weeks, many of the images will have different capture dates and only those scanned on the day of the first image will be correct.
I had a solution which suddenly has stopped working and I'd like suggestions as to why.
My solution was to import the images into Elements, and change the date there. Element will allow you to say the day and time are unknown. Then I would remove the images from the LR catalog (do not delete from drive) and import them back again. Voila, problem solved. LR would give all the images the same date and set the unknown time to 12:00:00 AM.
Now this appears to no longer work and I wonder why. When I look at the image in Elements it has the date I entered which may be decades ago. The same image imported to LR has the date the image was scanned. Obviously the date entered into Elements is in the file somewhere, but LR will not show it on the thumbnails. LR now shows the time scanned while it use to show the same time as shown in Elements.