Just out of curiosity, where are you located. I live in the state of Idaho, USA. (Not that it makes any difference.) I could not find Duncan in the 1851 census either. I mentioned this to a friend I had made in Scotland through the research I was doing and he provided me with what I sent to you. I got the information from Ancestry. I don't know why it's not on ScotlandsPeople.
I still haven't figured out what happened to Duncan. I'm assuming that he emigrated somewhere, maybe Australia or New Zealand. If he stayed in Scotland there should be some record. I haven't found any records about Duncan beyond the 1861 census and it doesn't make sense.
If I find anything, I'll let you know
From: Islay@Scotland-Genealogy.groups.io <Islay@Scotland-Genealogy.groups.io> on behalf of mearnsmg@... via Groups.Io <mearnsmg@...>
Sent: Tuesday, February 18, 2020 1:27 PM
To: Islay@Scotland-Genealogy.groups.io <Islay@Scotland-Genealogy.groups.io>
Subject: Re: [Islay] McAulays
_Hi Hi Paul,
I use Scotland's People a lot, but Duncan does not show up on the 1851 Census. I have sent a query into Scotland People. Ideally finding Duncan's death record could give us his parents and the possible connection.
Apologies as you probably have this already, I have found an Angus McAulay 26 (plasterer born Edinburgh) & Catherine McAulay 22 (Power Loom Weaver born Eastwood Renfrew) at 6 Catherine Street in the Parish of Calton (Glasgow) in the 1851 Census, but no children