Thanks for getting back to me David. Yes, the probate documents are very interesting - as you state, there are two sets available online via the Missouri State Archives - one for William and one for his first wife 'Ida E Burroughs' who pre-deceased him. I first discovered these some time last year.
As you also state, the documents refer to William's wife as 'Nina K. White' (his second wife). Nina married a man named White AFTER her marriage to William. It is Nina's marriage to William which interests me, as I can find no record of it. I have thus far been unable to locate Nina's maiden surname, and I wondered if anybody might have access to the St Louis Post-Dispatch database, as I can't access it from the UK. I wondered if there might be any references in there to the marriage of William and Nina, during the period 1896-1898.