Every item has a unique SKU — a 3-letter prefix plus a 4-digit number, like CFB0001. The barcode on the tag encodes that SKU.
Don't move a printed tag from one item to another. The barcode is tied to the original item, so it would ring up as the wrong piece at the register.
If a tag is lost or damaged, just open the item and reprint it — the SKU stays the same, so the new tag is identical.