Can I Fix the Dates on a Shared Album?
Photos other people added to a shared album export differently. Here is what you get and what can be recovered.
Shared albums do export, but what you get depends on who uploaded what. Photos you added come with their own .json files. Photos other people added may come with less information, and sometimes none at all.
Where a .json exists, the original date is in it and can be restored exactly. Where it does not, the photo may still carry its own EXIF from the camera that took it, which is just as good.
Takeout JSON Metadata Fixer uses the .json first, falls back to the photo's own EXIF, and tells you which photos it could not date. You can then set a date by hand for just those. Free for your first 500 photos.