He was asking about his 4.2.1 that had 4.2.1 when he bought it. And the answer is no, you can't use the untethered or go back to 4.1. I'm in the same boat as you, tethered right now, and since no SHSH saved but 4.2.1 right now, we both have to wait till a JB for 4.2.1 or higher comes out.
I had my old iPhone 4 with 4.0, 4.1, 4.2b3 saved, but had to swap it because the home button stopped working all together :-( Oh well, tethered really isn't that bad, I've been on it for 3 weeks and only rebooted once at my choice.