That's odd 12F and 58Y, when article on Delta.com states 12F, 20C+, 38Y.
https://news.delta.com/delta-and-bom...ement-aircraft
Delta has entered into an agreement with Bombardier to purchase 20 CRJ900 aircraft that will replace older regional jet aircraft flown by Delta Connection operators.

The operationally efficient jets are to be delivered beginning in late 2018 with the last delivery to occur in 2020. They will feature Bombardier's new Atmosphère Cabin, including increased carry-on bag capacity, a larger lavatory and improved aesthetic detail throughout the cabin.

These aircraft will be configured with 70 total seats including 12 in First Class, 20 in Delta Comfort+ and 38 in the main cabin. They will fly on small market routes to and from Delta's domestic hubs.