I just wanted to post the official wording from Delta in case anyone was interested:
On September 9, 2017, the Delta-marketed Premium Economy inventory classes for flights operated by Delta’s Joint Venture (JV) partners Air France (AF) and Alitalia (AZ) were reassigned from W to P, A and G. Delta-marketed fares for Premium Economy services offered by AF and AZ will use classes P, A and G for travel on or after September 25, 2017.
Please note: There are no changes to AF or AZ-marketed Premium Economy fare products, and all flights affected by this booking class reassignment are in the trans-Atlantic market.
[...]
Delta customers who were booked in Premium Economy on DL-marketed, AF- or AZ-operated flights in W class departing on or after September 25, 2017 have been re-accommodated to G class. Converted PNRs were updated via normal schedule change processing.
*Bolding mine
Source:
https://pro.delta.com/content/agency...ice-chang.html
I guess that clarifies what happened.