So you have 6.2 nand but ealier boot0/1, if they're incompatible it's what stopped your console from booting. Since you can't restore the previous nand, you should backup the current one and keep it safe too, maybe you'll need to recover from that.
He downgraded from FW 6.2 to FW 6.1 by restoring his boot0/boot1 backup on his system NAND. He can theoretically boot CFW via Hekate but for whatever reason it is not working for him.