@userWL24JwrWDs Since relying on the file timestamp in the operating system can always be troublesome for photos and can cause issues as you describe, photos have EXIF (meta) data stored inside the photo file itself.
I recommend that you look at file photo renaming tools that can use this EXIF (meta) data stored inside the photo files to rename the file. Using one of these tools you can quickly batch rename a lot of files. Then you can use the file name to quickly identify the proper place in history for your files.
"Thank you for your response. However, I'm pretty sure it is the meta data that has been changed already during the download process."
I'm pretty sure that is the file creation date, not the meta data. Download an EXIF tool and check the meta data.