When I received a computer first, Windows 7 was installed and I reinstalled Windows 10. Now I would like to install Windows 7 again.
How can I Windows 7 OCEM product number?
How can I install the Windows 7?
The COA is shielded from fading under the battery. Here is my E5510.
You should however use Dell OEM System Locked Preinstallation and install Windows 7 using a UEFI Boot (requires the latest BIOS update A16). See here for details:
Windows FAQs and OEM Downloads