Re: Maiden Name or Married Name
I have never heard of anything quite so formal.
It is perfectly true that a married woman in Scotland doed not legally change her surname. In all later documents she is formally referred to as 'xxx yyy or zzz' where 'xxx' is her given name, 'yyy' her own maiden surname and 'zzz' her husband's surname. She may of course had had more than one husband, so 'zzz' could be 'zzz1 or zzz2 or ....'
This is why the mother's maiden surname is usually included in baptism records (if the mother is named at all!), why the gravestones of married women usually show their maiden surnames, and why married women are indexed by maiden surname and the surnames of all husbands in the Scottish death indexes, assuming that the informant was able to supply all this information of course.
It is unusual for a married woman in the 18th century, and even the early 19th, to be referred to be her husband's surname. I have seen many baptisms like this one: "1748, September 11th. William lawful son to Alexander Leslie of Balnageith in Burncrooks and Mrs Anne Duff his spouse was baptized." [Rothes Parish Register] or death notices like this one: "Died at Newton of Duffus on the 3d inst Mrs Margaret Mason, relict of the late Mr William Leslie, tailor there, aged 85." [Forres, Elgin and Nairn Gazette]
Mrs, the abbreviation for Mistress, would have been fully pronounced as 'mistress', not 'missis', and the full title was applied to all women, married or single. Think of Carolina Oliphant's poem,'The Laird of Cockpen' when the proud pompous self-important suitor comes wooing and says "Gae tell Mistress Jean to come speedily ben ..." (full text at https://www.scottishpoetrylibrary.org.uk/poem/laird-o-cockpen/, and sung by Kenneth McKellar at https://www.youtube.com/watch?v=vLYP7I9rVFU)
In some early census records wives are recorded by their maiden surnames, and widows even more frequently. They also remarried using their maiden surname, like this example: "1834, 26th June. James Hay merchant in Arbroath and Margaret Sang, widow, residing in Timber Market in this parish were contracted in order to marriage and having been regularly proclaimed were married the 30th June." [Brechin Parish Register] Margaret Sang was the daughter of Alexander Sang and his wife Margaret Mill, and the widow of Andrew Watt, whom she had married in 1812.