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

Or is it?

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

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.