Genuine part numbers are owned by the car companies for parts they have made.That is why most aftermarket companies make up their own part numbers as an alternative. They can say it "replaces or suits" a genuine part number but should not use the genuine number and so infer it is the same part. Many companies that use a genuine part number have been taken to court and either had to renumber or destroy their copy parts. The car companies may allow some use of their numbers by agreement betweeen them and a parts supplier.Rare Spares has this arrangement with GMH for some parts but also uses their own part numbering system for the majority of parts, such as kits.