In today's video I will show you how to save the SHSH2 blobs for future downgrades on the devices that require BoardConfig (like iPhone 6S, 6S Plus, SE). These devices require a special command / method in order to save the blobs. It you use the normal method used for iPhone 5S and 6 /6Plus, you will get "iOS 10.2.1 IS NOT SIGNED". That's in fact not true, at this moment, iOS 10.2.1 is the latest version so it is signed, but in order for the blobs to be valid and usable for downgrade, you must make sure your device's board configuration is set. Only iPhone 6S / 6S+ and SE require the board config due to the fact that these devices come with either TSMC or Samsung chip (the board code being changed accordingly).
Saving blobs is very important if you want to downgrade, and considering the fact that we might not see a new Jailbreak in a long long time, I highly recommend you to go almost any lengths to downgrade from iOS 10.2.1 or iOS 10.3 back to 10.2. Please address to the previous video for more information about downgrading from iOS 10.3 Beta 1 back to iOS 10.2 without Jailbreak required.