Hi there. I am buying a bunch of 8TB Seagate Ironwolf Pro HDD's for my NAS. 8TB. Per Seagate's website there are three versions available, ending in serial numbers001, 0004, or 0021. Please can you help to explain the difference to me? Amazon has the 001 and 0004 and claims the 001 is an updated version of 0004. would like to understand the difference before I order.