The date reset does not change the installer that you have available.
If you are booted to internet recovery (you booted with Option-Command-R), then that will usually offer you the system that your Mac originally shipped with. Sounds like that would be Lion for you.
If you want to update to El Capitan (or need to do a clean install of El Capitan), then the best method is to download the El Capitan installer app first. Use that app to make a bootable installer on a USB flash drive (or a small partition on an external USB drive - there's lots of choices here). Boot to that El Capitan installer, where you have to use the terminal to change the system date (and your command is OK for that), and THEN you will find that El Capitan will install.
If you need to download the El Capitan installer, Apple support has a download link for that, among other macOS installers: https://support.apple.com/en-us/HT201372
The linked page also describes how to make the bootable installer in your terminal.
If you are booted to internet recovery (you booted with Option-Command-R), then that will usually offer you the system that your Mac originally shipped with. Sounds like that would be Lion for you.
If you want to update to El Capitan (or need to do a clean install of El Capitan), then the best method is to download the El Capitan installer app first. Use that app to make a bootable installer on a USB flash drive (or a small partition on an external USB drive - there's lots of choices here). Boot to that El Capitan installer, where you have to use the terminal to change the system date (and your command is OK for that), and THEN you will find that El Capitan will install.
If you need to download the El Capitan installer, Apple support has a download link for that, among other macOS installers: https://support.apple.com/en-us/HT201372
The linked page also describes how to make the bootable installer in your terminal.