Originally Posted by quantumrand
Since you installed the ICS update manually using the link in the OP, it'll say I9020XXKI1 (possibly I9023XXKI1, but I don't have an I9023, so I can't say for certain) no matter what, since that's the radio the update flashed to your device. The fact that the update let you install it at all suggests that you do indeed have either the I9020T or I9023.
The only way you could flash the current 2.3.6 to 4.0.3 update on an I9020A would be if you had a rooted phone with custom recovery image, which I'm assuming you don't.
That stock 2.3.6 update I linked you in my last post should almost definitely be for your device. What I don't know is whether or not it will actually let you install it coming from 4.0.3 with the stock recovery image. If it does let you install it, there's very little chance it will break your phone. If it doesn't let you install it, it'll give you an error before making any changes and stop the installation automatically.
If you do attempt to roll back using that file, let me know how it goes. It will be useful information.
I am not so good at knowing that, but I think my unit should be some I9020. It was originally bought in the UK, just several weeks after they started selling Nexus S so it must be an early version of it. The update came OTA, I did not install it manually, that's why I wrongly assumed it must be pretty safe to do it, did not expect so big issues...
Final question - I have not done it before - so what is an advised procedure step by step before I actually try to flash the GB update if I want not to lose the apps and especially the data (e.g. notes, pictures etc in some apps)? Thanks!