Finding out device serial number

Hi, I have bought an iphone 6 logic board which had iphone error 40. I removed the nand and tested it with ipboxv2 and it says Unrecognized Nand_Flash..

So I think that the nand is faulty as iv only seen this error before on bad nands. The problem I have now is I can replace the nand, as I have plenty spare and do it countless times on ipads, but I dont know the serial number, so if I write a new serial number to a new nand it wont activate ?. Is there anywhere on the logic board where the serial number is, or any way ipbox can retrieve it from any other ic etc, I know its written to the baseband, but cant think of anyway of retrieving it. I have asked the seller if he still has the original case with imei, so will see if he comes back with anything.