In response to my post re using (for example) Mary Smith, nee? when I don't have Mary's maiden surname, Vyger wrote with regard to sorting: 'I see how your method works and like all the other methods it has it's merits particularly in sorting however it is now accurate, Smith,nee is not the same as Smith etc." [I assume that was meant to be '...not accurate...'?
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I had mentioned earlier in my post that using 'Smith, nee?' keeps all the wives with unknown maiden names together at the end of their particular families' alphabetical list of entries in the Person Index. I suppose I should have made that clearer. By using the 'Smith, nee?' method, I am still keeping the wife with the unknown surname ordered within close proximity to all the other Smiths, although of course they will appear at the end of that list of Smiths. So, for example, 'Smith, Zander' would be followed by Smith, nee?, Ada', etc.
Using the ',nee?' at the end of the married name makes it very easy for me to find my particular Mary in the index, rather than having her in a long list of other Marys with blanks instead of surnames, as their maiden surnames are as yet not found. And let's face it, may never be! In which case they would languish at the beginning of an index forever. Out of curiosity, I just did a 'NameFind' search for 'Mary', surname 'nee?' and there are 47 matching entries in my tree of nearly 10,000 folk, albeit often used with other given names as well. When added to all the other 'nee?' women who do not have Mary in their names, the blank surname list would be very long. Needle in a haystack time! 
I know it might not be proper, but I feel that our MNU women deserve to have a surname attached, even though it is their husband's. I spent only 16 years with my maiden name, then 50 years with my husband's name. So his surname is very relevant to me. I wouldn't want me to be nameless just because my maiden name was not know!
Also, I would hate to have to put alternate names for all those people who are missing their maiden surname! 
Vyger, I found your LNU, MSU and MNU information fascinating. With all those millions of records using these various acronyms, I am surprised I have never come across them before. Thank you - I found your whole post very interesting! 
Kind regards,
Michele