Apple has allowed iPhone 4, 4S, 5 and 5c activations after downgrading

According to Reddit, Apple has enabled active when returning to the old iOS version without changing the wifi address if you want to downgrade.

This only applies to machines running A4, A5, A6, and A6X CPU chips.

1. iPhone 4, iPod touch 4 and iPad 1 are equipped with 1GB Apple A4 CPU.
2. iPad 2, iPhone 4S and iPad Mini are equipped with Apple A5 CPU, code name S5L8940.
3. iPhone 5 and iPhone 5C are equipped with Apple A6, S5L8950 code name.
4. 4th generation iPad series equipped with Apple A6X.

If you want to downgrade to iOS 6.1.3 or 8.4.1, the users can easily activate the device if you use iPhone lock.

A reddit forum member returned to iOS 9.3.2 successfully (with SHSH Blobs saved).

Also, if you can save SHSH2 Blobs, or save SHSH2 Blobs to restore during the last Apple unlock, you can now go back to that iOS version and work well.

1. The way to downgrade from iOS 10.2 to 10.1 does not lose data
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3. The iOS 10.1 downgrade guide for iPhone / iPad has lost battery