Is is true that if they were non-conformists or Catholics that the births may not have been registered?
Can-of worms time, I fear.
First, none of the births could have been
registered because they all occurred long before the start of civil registration in 1855, when birth certificates were introduced in Scotland.
Second, the term 'non-conformist' was coined in England and specifically means someone who did not conform to the Church of England; it would apply to members of all presbyterian denominations. It is accordingly meaningless in relation to Scotland, even though it is (regrettably) sometimes used as if it were.
Yes, it is true that many of the baptism records of Catholics or of adherents of the numerous breakaway denominations in Scotland have not survived, and a few of those that have survived, along with baptisms in the Scottish Episcopal Church, are not available online.
However it is also true that the records of many baptisms in the Church of Scotland have not survived either, so the absence of a baptism record doesn't really tell you anything.
