In addition to this, I am confused as to just where LDS patron submissions to the IGI get their BMD's from? Are they non conformist church records or are there Church of Scotland OPR registers missing and/or available somewhere else?
IGI stands for International Genealogical
Index and it doesn't contain any
records at all, in spite of their terminology. It is an
INDEX, no more, and every piece of information there is secondary information. It is a fantastically useful resource for locating
records, but not to be relied on as autoritative.
You have to click on each listing and look at the detail. Many of the 'patron submissions' and the 'community contributed' listings are duplicates or near-duplicates of the 'community indexed' ones.
My rule of thumb is that if it's 'community indexed' in the IGI then it's usually correct and can be used, with the intention of checking the original document to verify it in due course.
If it's 'community contributed' it's possibly correct, but has to be checked carefully against its original document. Some patron submissions are from excellent and well-documented genealogies but some are pure fantasy. (For a moment's amusement, see
https://familysearch.org/pal:/MM9.2.1/9S3D-KY4 and
https://familysearch.org/pal:/MM9.2.1/MR15-DNZ)
If it's 'patron submitted' it's not to be trusted unless and until I can track down the original document from which it was taken, and assess the reliability of that as a source.
There are records not included in the IGI, for example last time I looked the baptisms in the parish of Duffus in Moray between 1820 and 1854 are missing for some reason, and I have heard that in some parishes all the boys' baptisms are listed but not the girls', or
vice versa.
In Scotland, the registers of some denominations other than the Church of Scotland are not included, or not completely included. Some churches will not give permission for their registers to be filed or indexed.
The only absolute certainty is that anything found in the IGI or any othe online index or genealogy must be treated as a finding aid only, and carefully checked for authenticity and accuracy.