Who is 'they'?
EBay would have the same listing number on a listing where there were multiple items for sale. For example a seller who has 20 identical copies of a sweater.
EBay would have a different listing number on each listing if those 20 sweaters were each listed separately (which eBay doesn't allow, but bear with me).
The seller might have a different stock number on each of her 20 sweaters for her own use. This might appear somewhere in the title or the description, to help her in pulling the item for shipment.
