Hi Bry
This is what I found in WALES
1871
Minera, Bersham, Denbighshire wales (RD~ Wrexham)
Williams Square
Nicholas STEVENS head mar 36 lead miner b St Agnes
Ann wife mar 36 b St Agnes
William J son unm 14 lead washer b St Agnes
Mary A dau unm 10 scholar b St Agnes
Bessy dau 8 scholar b St Agnes
Sarah J dau 1 b Denbigh, Bersham
This is what we had in 1861 in Cornwall....
Hi all 
St Agnes, Cornwall
Nicholas Stephens head mar 27 tin miner
Ann wife mar 27
William son 5 scholar
MARY A dau 3
Sarah dau 2 months
all born in St Agnes, Cornwall
deb
Do these children add up with what you have in 1881 and 1891 in Scotland ...let me know . Also I will check to see if Sarah , who is 2months in 1861, died or is she with someone else?
deb

ps I will find all the other Stephens/Stevens b St Agnes ... I think they are siblings or definitely relatives of Nicholas .