Hi Paul.
Thank you for sharing your question. I understand how annoying it is when photo memories pop up with the wrong dates, totally messing up your attempts to relive specific days.
Based on my knowledge, Microsoft sorts and photos show in On This Day using when the file was changed or uploaded. It's not a mistake, but how they planned it. Often, phone uploads mess with the original date info, mainly if photos come from apps like WhatsApp or Signal or if you use the Camera Upload thing.
Please follow these steps.
I suggest using the OneDrive computer app to keep the correct dates and make On This Day more accurate. If you copy photos to a synced folder on your computer, the original date info should stick around. Phone uploads often lose this info.
May I also ask how do you usually upload photos to OneDrive phone, computer, or browser?
I hope this answer is helpful, if you have any questions, feel free to reply.
Best Regards,
Noel