Server or client, every supposed prefetch would be unique. If I trick an LLM client into grabbing:

site.com/random-words-of-data/image.gif

Then:

site.com/more-random-data/image.gif

Those are two separate images to the cache engine. As the data refreshes, the URL changes, forcing a new grab each time.

For email, marketers do this by using a unique image URL for every recipient.