I’m still confused what you done to get exif data away… aren’t it RAW files ? Those should always have it , and i know of nothing that thinks it’s a good idea to remove it.
Maybe some exiftool tricks can be good for you ?
Like taking the filesystem date and putting it into exif in one of the fields .
Or the other way around , making sure the filesystem modified and/created date is set to the photo-taken field in exif.
Or, matching up original raw files by filename and copying missing exif data from those into jpg files that don’t have it . Etc…
I know the commandline can be scary , but it can be a great help if you need to fix things in 1000s of images.
Or at least try a tool or GUI to help you with this, don’t go entering date indo one by one :).