Scotland used to have forms of marriage known as “irregular marriages.” These were situations where the law regarded you as lawfully married even though you had not been married by a Minister of Religion or a Civil Registrar. (Marriage by Registrar didn’t exist in Scotland till 1940).
The law could consider a couple validly married if they lived together for a while and friends and neighbours regarded them as married. That was called marriage “by habit & repute”. Alternatively if you acknowledged each other as man and wife in front of a couple of witnesses, then the law considered you to be married “by consent”. There were also marriages by promise. (Details in the link below).
The key element was that you didn’t need a Minister or a civil Registrar to validate or record them. These irregular marriages were abolished in 1940, and replaced by Register Office ceremonies.
So in 1927, marrying "by consent" at the Blacksmiths in Gretna Green (or in other towns along the Scottish border) was a common form of irregular marriage. It was possible to later appear before a Sherriff and swear oaths as to the fact you were married, and if satisfied, the Sherriff would then order the marriage to be recorded in the statutory registers (which are now on the Scotlandspeople site). Such certificates will normally show that the marriage was recorded by Sheriff’s warrant, as opposed to the usual wording of “according to the forms of the Church of Scotland”, or the Roman Catholic church etc.
Unless your couple chose to swear oaths before a Sherriff, the marriage won’t appear in any official records. But it would still have been valid in law provided that they had witnesses able to testify to it. And in this particular case the judge in 1967 evidently ruled that it was valid.
You can still get married in Gretna Green today but nowadays the Civil Registrar performs the marriage, so it goes straight into the civil records.
See:
http://www.gla.ac.uk/schools/social...medicine/scottishwayofbirthanddeath/marriage/
Today we might call that type of irregular marriage a “common law” marriage, though that actual term has no legal meaning in the UK. But it describes the concept.