Tiny umbrella saved SHSHs ? where is the current one?

Before jailbreaking and unlocking my new (old bootloader) 3GS I thought it would probably be a good idea to save the shsh files I could see on cydia.
The previous owner must have pushed the "make my life easier" button, so I could see the firmware 3.1.3, 4.0,4.01, 4.2b3, in green letters on top of cydia.

So I just ran tiny umbrella and connected the iPhone, just pushed the "save shsh" button and a few minutes later I could see the saved firmware versions.

my questions:
1. where is version 3.1.2 ?
when I checked the iphone it said 3.1.2 is the current firmware.
But it was not on the cydia green writing list!
I can still install 3.1.2 over pwnage and keep the other shsh files as backup, right?
2. Now that I have saved the shsh files on tinyumbrella, does that mean I can up and downgrade between the saved firmware versions as I like and without upgrading baseband?
3. Are the saved tiny umbrella shsh files (over cydia) already jailbroken?
Or would I have to use pwnage tool on them for jailbreak and activation?