The answer depends on who the seller is and what the seller did.
if your brother bought it direct from an Apple-owned store, the date of your brother's purchase should be the effective date for warranty, etc. You can have your brother contact Apple customer support at the support number for the Apple online store for this non-technical problem.
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When bought through a small retail seller, it can be difficult for them to meet the more than US$250,000 minimum product purchases and many other requirements for each storefront to become an Apple-authorized Reseller. What Sellers do instead is band together into a buying group, to get good discounts for higher volumes of products.
What a buying group does NOT get is the ability to have the date of retail sale as the official date of purchase. That date becomes the date the buying group bought from Apple.
if a computer sits on a small seller's shelf for a while, the warranty might expire before the computer has been sold at what we think of as a retail sale.
There may be nothing you can do. But if there is anything that can be done, the Seller would have to do it on your behalf.