I purchased 4x$50 cards in a single transaction per the instructions above on 5/24. It billed to my Platinum as a single $200 transaction and I was NOT re-imbursed :-(.
However, when I booked my two tickets, the Delta agent via Facebook Messenger, used all 4 gift cards on one of the two tickets I bought and the balance due was $126. Amex credited me back the $126 so I "ate" $74 in this transaction but still have $74 I can use later. My advice, just make them 4 separate transactions to be safe.