However, it is preferable for the manufacturer to assign the number. As different suppliers may provide identical items as seen by the consumer it is possible that items that are apparently identical have different GTINs. This can affect the organisation of computer files. Examples of such items are plasterboard, candles, drinking glasses etc. When a product is made specifically for a customer and orderable only by this customer, it is permissible for a GTIN to be assigned by the customer, using the customer's prefix.
Some Companies produce the same article in several countries, or in several plants.
In this case the GTIN should be allocated centrally and managed by one of the companies in the group or one of its production facilities. This implies that each variant must be assigned a different number whenever the variation is, in any way, apparent and significant to any partner in the supply chain, to the final user or to the retail customer. What is understood to be an apparent and significant variation may differ from industry to industry. This list is not exhaustive. Once it has been defined, the GTIN of the trade item must not change as long as the characteristics of the trade item do not change.