With downgrade rights you do not get a new unique Windows 7 Professional product key. The Dell OEM System Locked Preinstallation (SLP) Key is used which activates offline automatically if and only if a valid Dell BIOS is detected. A system which came with Windows 8.1 Professional is deemed to have such a valid BIOS. More details here: [URL]  If you have retail media you can apply Dell OEM SLP activation: [URL]#OEMSLP
I am of the understanding there is a downgrade option for a free CD key if downgrading from windows 8 to windows 7.  I am in the process of doing this because I have lost everything on my computer 3 times since purchase in a year and a half.  Only option from Dell was to re-install my OS.  Now I want to get rid of Windows 8.  Can you advise on this.  I'm hesitant to post my  Service Tag here. Thanks. Mike Murphy
Downgrade from Windows 8 to Windows 7