Hello! I recently got an Amex Platinum card, my first travel rewards card after decades of cash back cards. I'm having trouble figuring out how the airline credit works, and was hoping someone here might have answers to my main questions:

- I was approved/received the card in May; does that mean I have to use the $200 airline credit by the end of the year, and in January a new credit will be available to me to use in 2026?
- I have two Delta flights booked in the next few months, but I purchased them on a different credit card. I feel fairly certain that drinks/food I buy on the flights will be reimbursed via the credit as long as I pay with my Amex Platinum, but can I upgrade my seats from Main to Comfort+ now using the Platinum and have that cost reimbursed via the airline credit? (Or show up as a statement credit?)

Also, when is the airline selection made each year if we want to change it? Since I've got two Delta flights booked already this year I was going to select Delta for this year, but next year I was going to swap to United so I could use the TravelBank (I often fly both airlines about equally, but I already know for sure I'll be taking more United flights next year.)