I just discovered, thanks to @09c6e1eb from The Wayback Machine that there is a button, "About this capture", that actually details the 'files from the future' in a Wayback copy of a webpage. I had never clicked that before! For my Cybercultural post today, I had manually inspected the source code to see which files were from the future. But this button is very useful going forward.

https://files.mastodon.social/media_attachments/files/111/177/694/459/021/942/original/c85b571fd89c7e2c.png 

 Also, this is known as "temporal cohesion" and there is an Internet Archive paper about this: https://archive.org/details/arxiv-1402.0928