Reverting to original copy in Numbers

If you're on the Mac try going to:

File > Revert to > Browse All Versions...

With luck you will be presented with a Time Machine like interface that allows you to go back in time and look at old versions of your document. When you find a version you want click the Restore button.

I keep my Numbers documents in iCloud Drive, so this works reliably for me.

SG

It depends...

Numbers automatically saves documents. To go back to a point-in-time usually requires that you made a conscious effort to save your document at that point.

Depending on how far back you need to go, you may be able to just Undo (Command-Z) the changes you made... Numbers keeps a history of actions and you can step back through them, although I'm not sure how far back this goes).

Alternatively, if you have Time Machine running, you can restore a previous version of your document from your Time Machine backup.