I'm an infrequent Delta flyer and new to having Delta as my airline for Amex reimbursement, passing on this datapoint fwiw. Several months ago I purchased first-class upgrades for two tickets, each upgrade costing between $100 - $200. Amex credits were not automatically applied. I inquired recently via chat, identifying these as "seat selection fees.". The agent took a look and said "I can see they these were for upgrades. It sometimes takes 8-12 weeks for credits to post (!), but if you like I can submit them for manual review.". Not sure whether that was a good idea, I tried to stall for time on the chat. Before I could reply directly, though, the agent came back and said "good news, they were approved.". And I have in fact now received the statement credit. I found it interesting that the agent was able to identify these in their system as "upgrades" and that I still received the credit anyway. YMMV.