No, I dont think thats the case. Your theory would make every single chip from AMD document essentially the same, as there are Athlons and Opterons with E0/C2 stepping.
What is likely the case here is, steppings clearly define (as per AMD table) slecific fixes. There are no Deneb E0 steppings, as the last one is C2, but there is E0 stepping for Thuban (6 core) and Zosma (Thuban with 2 cores deactivated).
They are new chips in Phenom family with specific codenames and changes to hardware level. They were released 1 year later then Deneb, and as such have fixes beyond C2/C3 steppings - hence E0 and new chips.
Basically,
Deneb 2009 C2 4 core chip
Thuban 2010 E0 6 core chip
Oberon 2019/06 B0 36CU chip
Oberon 2019/12 E0 60CU chip
Dont think thats the case, especially with info coming from the guy that leaked this first, AquariusZi, who said Oberon is going through constant steppings and is one size smaller then Arden.
If upgrade was additional 50-60mm2 I think he would not say its smaller chip. But lets wait and see