Anyways.. one of the points raised was that if your folk are on the 1841 as being born in the county, then it is very probable that your ancestors have lived there since the middle ages.
Apparently this is because population migration did not really start until the 1840's, before then people tended to stay in the village or town they were born in.
This would imply that if you have just assumed that "Joe Bloggs" in the OPR's is your ancestor because he lived in the right village at the right time.... the odds are he is indeed your man.
As I said, they were discussing this in the context for England.... but it might apply for much of Scotland
Jim