Excellent work but you are looking at Gretna (or Graitney) and no Gretna Green.
Gretna Green is
in the parish/RD of Gretna or Graitney.
Which would mean that there are lots of marriages (irregular) missing from the SP index.
Quite possibly.
Let us assume, for the moment, that it is true that one in six marriages in Scotland took place in the parish of Gretna or Graitney, mostly at Gretna Green which is in that parish. Then the total number of marriages of people with these ten commonest surnames in that parish/RD would be ten times the number of marriages actually registered, which is 9,749. So that, between 1855 and 2016, 97,490 marriages of Smiths, Browns, Wilsons, Stewarts, Thomsons, Campbells, Robertson, Andersons, Scotts and Macdonalds would have been performed at Gretna Green or in the same parish/RD.
I looked at the 1911 census data. The total population of Scotland was 4,759,445, and the ten commonest surnames accounted for 439,886 people, which is 9.24% of the population.
So assuming that the distribution of surnames in 1911 was not radically different from that in any other year, that would mean that the total number of marriages conducted in the parish of Gretna or Graitney was 1,053,946. Divide that by the number of years from 1855 to 2016 (162) and that would mean that 6506 weddings a year, or 18 weddings every day of the year including Sundays, were conducted at Gretna (Green) or Graitney.
This contrasts sharply with the remarks of the minister of Graitney, who in 1793 commented on the regrettable notoriety of his parish. "This parish has been long famous in the annals of matrimonial adventure, for the marriages of fugitive lovers from England , which have been celebrated here. People living at a distance erroneously suppose, that the regular and established clergyman of this parish is the celebrator of those marriage; Whereas the persons who follow this illicit practice, are mere impostors, priests of their own erection, who have no right whatever, either to marry, or to exercise any part of the clerical function. There are, at present, more than one of this description in this place. But the greatest part of the trade is monopolised by a man who was originally a tobacconist, and not a blacksmith, as is generally believed. He is a fellow without literature, without priciples, without morals, and without manners. His life is a continued scene of drunkenness. His irregular conduct has rendered him and object of detestation to all the sober and virtuous part of the neighbourhood. Such is the man (and the description is not exaggerated) who has had the honour to join, in the sacred bonds of wedlock, many people of great rank and fortune from all parts of England. It is 40 years and upwards since marriages of this kind began to be celebrated here.
At the lowest computation about 60 are supposed to be solemnized annually in this place."
The '40 years' is about right, because the practice began following the passing of the Marriage Act in 1754, which required all marriages in England and Wales, except those of Jews and Quakers, to be celebrated by a priest of the Church of England.
The minister in 1834, in the News Statistical Account, also referred to iregular marriages. "The far-famed marriages of Gretna Green are celebrated, it is said, to the number of three or four hundred annually." That is a long way short of one in six of all marriages in Scotland.
I am not taking issue with anything else in this thread; merely attempting to debunk the assertion that one in six of all marriages in Scotland wer conducted at Gretna Green.