I pushed 147 updated posts to my scheduler. Every one still had the old images, because the upload step remembered files by name and all my carousels use the same file names.
The check
After any update, download one live image from the scheduler.
Compare it with the file on your computer. Look at it, or compare file fingerprints.
Do it for every platform, not just one.
The fix in my upload script
Remember uploads by the file's contents, not its name. A file with the same name but new contents then uploads again.
Why it's easy to miss
Dates, slide counts and states all looked right. "147 updated" is not proof the artwork changed.