For further explanation, DL shifted from using F/P/A/G fare classes for domestic First Class to J/C/D/I/Z classes (which are the same classes used for Delta One) back in 2018/2019. This freed up the P/A/G fare classes for use with the DL Premium Select premium economy product. You may see older sources that still refer to the J/C/D/I/Z classes as Delta One, but this is no longer true.