Can I Fix the Dates on Scanned Family Photos?
Scans are dated the day you scanned them. Here is how to set the real decade in bulk.
A scanner writes today's date, because today is when the scan was made. So a box of prints from the 1970s comes out of the scanner looking like it was all photographed this afternoon.
If you scanned them into Google Photos and corrected the dates there by hand, that work is not lost: your correction is in the .json file in your export, in the photoTakenTime field. A tool that uses the wrong field will throw it away and date everything to the year you uploaded, which is the single most common way this goes wrong.
The app uses the corrected date, so the work you already did survives. For scans you never dated, you can set a date and a place across a whole batch at once, which is how you get a box of prints into the right decade without opening each one. The first 500 photos are free, which is enough for a decent-sized box.