Ticket value and expiration date
 

I purchased a ticket for $323 and change on Oct 2022. Ended up cancelling the ticket in early 2023 but then purchasing a much more expensive ticket in March 2023 with that e credit and credit card. I was now looking at cancelling and called Delta to see what the expiration date of the credits will be. My expectation was the $323 would expire 12/31/23 and the remainder in March or maybe Dec 31 2024. Delta said no, the entire amount expires 12/31/23. Is that correct?

Yes that is correct. Tickets normally expire (all travel completed) by one year from original date of issue. During Covid, Delta extended Covid tickets that were to expire in that one year limit to expire on December 31, 2023. You could travel after 12/31/23, but you had to book prior to that date. If you booked and later changed the dates in 2024, the tickets would have no value.