The developer behind Sn0wbreeze jailbreak tool, iH8sn0w,is currently working on a utility which will allow users to extract and save SHSH blobs for previous iOS firmwares.It is known that TinyUmbrella and Cydia makes the same job. In case of TinyUmbrella and Cydia, both of them saves SHSH blobs of the firmware for which Apple firmware signing window is open.But you can’t because Apple stops signing the previous iOS version after a new one is available.
The utility which is being developed by iH8sn0w will allow you to extract and save SHSH Blobs of older firmwares. That’s why this utility is different from TinyUmbrella and Cydia. If you have missed saving hashes for your iPad, iPod Touch and iPhone then this utility will definitely help you in case of untethered jailbreak.