This info is based on tips from our readers who received the update on their dev preview devices in Europe and US (Verizon). Lumia 930 in Europe and Lumia 928 on Verizon have received firmware updates, as the incoming OS version in Lumia Denim is same as PFD, 8.10.14219.
Other dev preview enabled devices like Lumia 520, Lumia 620, Lumia 625, Lumia 530, Lumia 720 etc, won’t get the firmware update and hence there may be no update for them at all. We have explained this here.
Lumia Denim roll-out status:
Rolling out to Lumia 520, Lumia 530, Lumia 620, Lumia 625, Lumia 720 etc in many of the African & Latin America markets
Rolling out to Lumia 520, Lumia 530, Lumia 620, Lumia 625, Lumia 720 in many of the Asian markets