QUOTE(epsonstylux @ Nov 23 2011, 05:34 AM)
No you can't. I tried doing that to my sister in law's phone. she was on 4.2.1 and never upgrade to 4.3.3 although she has cydia, there is no SHSH saved.
btw any idea why iphone 4 has jailbreak while 4S didnt?
The way Cydia automatically saves the SHSH is that you need to open Cydia a couple of times DURING the period Apple is Signing the firmware version.
For example, if you are jailbroken on 4.2.1 and never upgraded to 4.3.3 BUT, during the time Apple was still sigining 4.3.3, you opened up Cydia to update some tweaks, to download new tweaks etc, most likely Cydia will then automatically try and save your SHSH.
This was how it worked before. The easiest way to check is to open up Cydia now and see what SHSH is saved (you will see at the top of the Cydia window). If no 4.3.3 is mentioned, then, most likely it was not saved. But Cydia sometimes does not display it as well even though it saved it so download TinyUmbrella and in the Advance Tab, check the box that says "Requests SHSH from Cydia". Click on "Saved SHSH" and see what the messages that pops-up. If Cyida has the SHSH, then TinyUmbrella will get it for you and save it locally.
If TinyUmbrella says that Cydia does not have the 4.3.3, then that's that .... you cannot restore to 4.3.3 EVER.