Thank you for the clarifications. Generally speaking however, the domestic flights which are upgrade eligible and flown without Delta One service but in a Delta One cabin (ATL-LAX etc) are marketed as First Class.
Which Central America and Caribbean flights have recliner seats but aren't marketed as First Class? For example, ATL-BOG and ATL-SJU are both marketed as First Class. They only show up as Business class if they're booked as part of an itinerary (TATL for example) that includes Delta One. Either way, they're upgrade eligible.
You're right - many of those have been re-branded as First (though they still keep the Business Class fare codes (J, Z, I).
That wasn't always the case, but it's a good change. Will keep the confusion down.