There are plenty of threads on the DL board about "A" fares. There are apparently a few actual A fares, but the vast majority of what's sold as A is really a lower fare basis that books into A (e.g., MA00UPNA).

To find the true fare basis of an A fare on DL.com prior to purchase, you need to click "View change & cancellation policies." on the "Trip Summary" page that appears before you pay.

On DL, however, the main issue FTers have with A fares is being rebooked into Y during IRROPS. A fares on DL do earn class-of-service bonus regardless of what the "true" fare basis is.