There is a Q&A as part of the FAQ that Delta posted about this exact topic.
DL tried to pre-empt some of the cards to be mailed and sent out a batch in September before accounts were merged. If you receive a package with the wrong elite level you're not to worry...a new package has been sent out. DL has mailed thousands of them this week (supposedly) after the accounts merged to anyone who has a change in elite level.
-RM