Some bullion carries serial numbers, usually stamped on the bar or shown on an accompanying assay card. Whether they matter depends on what you're using them for.
Authenticity considerations
Serial numbers can help support authenticity when combined with other checks, such as weight, dimensions, mint markings, and testing. However, serial numbers alone do not guarantee authenticity, as counterfeit products may copy genuine serial numbers.
Buyback pricing
Serial numbers don't change what we pay. As with all bullion, buyback is based on metal content, not markings. See What can I sell? and How is my sell price calculated?.
Record-keeping & auditing
Serial numbers may be useful for internal records, inventory tracking, or audit purposes (e.g. SMSF or business reporting), but they are not mandatory.
Disclaimer: The above is not financial advice.