Not what I've experienced.
My understanding of what happens:
Once you have Saved a document, giving it a name and a location, the Mac automatically updates that document at frequent intervals. When you next open that same document and continue editing it, the Mac continues updating the file to include those changes.
When the document you are working on is put through a Save As…, any changes you have made up to that point of the current session will hav already been automatically saved to the original file. Save as… saves a copy of the document, as it currently exists (including thee changes up to then in the current session, with a new name or at a new location or both.
At that point, you have two copies of the same document in the same state.
Numbers breaks the connection with the original document file, ending the automatic updating that has taken place until this point, Any further edits are applied to the newly saved version. The original retains the changes made up to the time of the Save as…, but is not updated a further changes are made to the now current document.
If you want the originally saved version to remain unchanged, then immediately on opening the document Save As….
Then begin your editing on the Save As… copy.
Regards,
Barry