J/C/D/I/Z are used for First Class/Delta One. Initially, Comfort+ only booked into W class. S booking class was added more recently. DL Premium Select books into P/A/G fare classes. Basic Economy and Comfort+ have Fare Basis codes which start with coach fare classes as the fare filings basically mirror the main cabin fares (although Basic Economy fares only mirror main cabin fares up to a point). There's a dual inventory check when booking Basic Economy and Comfort+ fares and there must inventory in both their booking class and the underlying coach fare bucket (so when they zero out one of the coach buckets, it automatically moves you up to higher Basic Economy and Comfort+ fares along with a higher main cabin fare). Domestic FC fares also use coach fare classes for fare basis codes and have dual inventory checks. Earnings are based on the booking class (not the fare basis class).