How do you know that there were not multiple couples with same names? Current Challenge that is wrapping up I was helping find George Wallace sources for parentage. I found at least 3 or 4 couples of George and wife Margaret, with multiple born in the same place in Scotland, but with concurrent census with different children in different locations later in life, that proved there were multiple.
With Scotland, the earlier records are church records, so if they were not attendees of those records, then there are no records for baptism, marriage, etc.