If you load up Cydia today you will notice that it is now showing your SHSH blob for iOS 4.2.1. It’s probably due to the recent release of RedSn0w 0.9.6b7, the long-awaited but complicated untethered jailbreak for iOS 4.2.1.
If you don’t see your 4.2.1 blobs in Cydia, maybe you should use TinyUmbrella and make sure you’re 100% ready for any eventuality.