If you wanted you could email someone the two nands, the one you updated with to get to this point and the one that worked, along with your cpukey and they can check that the image is good/bad and also tell you why it didnt work.
A bit more info on your xbox would be nice, and what you did and programs you used to create the updated image, also what model xbox is it? has the jtag got a non standard smc wiring, like aud_clmp?
As far as recovering from this bad flash, you should be ok aslong as you have not updated to an official dash higher than version 7371 and also not burned any efuses, if you have a phat xbox, you should have the r6t3 resistor removed or disabled in some way as protection, then prevent live access via dashlaunch and family restrictions.
It will probably be cheaper for you to send your box off or take it to your local system mod shop for a repair than to buy all the equipment yourself.