Thanks once again for your reply. Yes, I'm aware of the earliest surviving parish records (Errol, Perthshire).
I don't have Moir's in my own ancestry. The point of my e-mail was just to highlight to those new to genealogy that statutory records of births/marriage and deaths; census returns; and parochial records are not enough in themselves to allow us to trace back beyond the mid-1700's with any degree of certainty.
Prior to that time, and if we are using those sources only, then we can only make assumptions, albeit in many cases educated assumptions (for example if the family lived at the same farm for several generations).
As you've pointed out, there are of course exceptions, and you are correct in that multi-generational gravestones, wills, sasine records, poor-law records etc can occasionally provide the required information. Sadly for the majority of working-class families these are the exception rather than the rule. You seem to have been fortunate in that respect - allied with the time and hard work you have put into it !
Thanks again for your replies, and good luck with your quest.