Indeed. It’s not possible stop the world and snapshot the entire internet in a single day.

Or is it?

You can trivially maximal bound it, though. If the training finished today, then today is a cutoff date.

That's... not what a cutoff date means. Cutoff date is an upper bound, not a promise that the model is trained on every piece of information set in a fixed form before that date.

you would have an append only incremental backup snapshot of the world