Just for a possible explanation on how that could be possible by a Scam referred to by Katana-San is when you purchase it at a retailer where they simply display them on a rack that is available for anyone to tamper with them. Scammers grab a bunch of cards off the rack and scratch/peel the sticker to get the code, then replace the sticker with a new one that can be purchased at Amazon. After they return the card to the rack, they just wait for someone to grab it and activate through the Checkstand. They will either spend that amount or sell that Gift Card either on a website or the dark web.
Ironically some of those same retailers will lock up products they sell where theft results in them losing money, but fail to protect their customers when the money is stolen from them. I would never recommend buying any type of Gift Card from one of those racks. That scam occurs right in the retailers store they are responsible for protecting your purchase and I have seen some cases where users where able to escalate the matter with the Store Manager, District Manager, and Corporate Office for a resolution, but it is better off not putting yourself in that situation.
Retailers are well aware of this scam and it has gone on for years. During the holidays we usually see warning on News outlets about this scam, but of course it can happen at any time. It is irresponsible for a retailer to pretend like it never happens and refuse to secure the cards behind a counter to protect their customers.
Katana-San provided the relevant information for you, just wanted to make you aware of how that can happen and avoid those types of retailers in the future for Gift Card purchases. I also recommend purchasing them directly from Apple where you can choose to have it emailed to you quickly or even the physical card mailed.