>, how would they know what my Apple account is until they’re redeemed?

To add context, your reddit post also mentioned: >, I purchased eleven Apple Gift cards from [...], and apple.com, and added the amounts to my Apple account.

I'm not saying the following applies to you but one can buy Apple Gift Cards using their Apple ID. After adding gift cards to the ecommerce shopping bag on Apple.com, it offers the option : "Check out with your Apple Account"

So Apple would know the exact AppleID at the time-of-sale instead of waiting until redemption. If for some reason Apple's fraud detection system doesn't like the transaction (e.g. unusual ip address from Mexico instead of USA, or too many high-value cards in a certain time period, or other black-box opaque heuristic) ... then the buyer puts their Apple account at risk.

Fraud prevention heuristics are insanely aggresive these days...

Last week, I bought a Netflix subscription and 5 days later, Netflix cancelled the membership for no apparent reason. I got on a customer support chat with Netflix and the agent said it was cancelled because of the credit-card #. It didn't pass their fraud prevention system and to try using another card. At least Netflix automatically refunded the entire amount back to me -- whereas Apple keeps the gift card balance for itself after locking accounts.

In another incident, I used a Chase credit-card at a physical Apple store to buy 2 iPhones on 2 separate receipts. The first iPhone sale was a success. The 2nd iPhone transaction just 1 minute later was denied and Chase locked the entire account. I had to call Chase customer service and recite the make & model of a car I had 20 years ago to prove my identity for them to re-activate the credit card!