Rebecca, you have the marriage cert for the marriage for Agnes Black and James McKechnie don't you from 1868? What was James' occupation and age, parents?
I have found the 1871 census entry yesterday. Not showing on the transcript I use but on SP. It shows:
Agnes McKechnie 31 stoker's wife husband at sea b. Lismore
John McKechnie 3 b. Glasgow
Elizabeth McKechnie 44 mother in law b. Kilbride Argyll
17 Brown Street Glasgow
There are also 1 boarder and 4 lodgers in the household.
There is the possibility that James Mckechnie could have died at sea? Likely between 1871 and 1881?
You mention the SP search gets in the way, what do you mean? Every time I've attempted to find Agnes/Ann I never get results, is there a trick to it?
I also can't find either of them on findagrave.
There have been major system changes to SP in recent weeks due to a change of company running the IT interface. It remains after the relaunch much more limited to search with

Previously, we could have searched for Agnes' death using both her maiden and married surnames and found her death entry relatively easily. You can't do that now. There are also other limiters to search fields which are very restrictive and don't easily provide the results index we had before. I couldn't see a death for Agnes so far under McKechnie in Argyll. Nor could I see an obvious entry for her on the index for the 1911 census.
If you haven't already, might be worth you searching for Archibald and family in the 1911 census. This would let you firm up his details further and give you the extended list of children from his marriages.
Findagrave is not that useful/complete really for Scotland. As suggested by Billy, best to start by looking around the area Archibald died and make local enquiries.
Monica
