Matters not. SA can NOT issue appointment without a nomination; it is a formality to be fulfilled and a box to be checked. With a LOA all you should need is DoDMERB and any nom from any source.
Having said that SAs may prefer to wait until all noms are issued Feb 1 in order to juggle their preferred [WCS] candidates vs principal nominees, NWL, recruited athletes, etc etc. vs available nominations.