Hi again, Annie! And thank you so much for your very helpful input, Ken!
Firstly, I've been having a look on the Irish BMD's. Having seen that William's father was a Maurice KEPPLE (deceased) on the 1912 marriage certificate, I noticed a death registration for someone of that name in Sept. quarter 1910 in Cork City, birth given as 1860, but no precise registration details given for his birth.
In the 1911 Census, at the address William gave as his place of residence on his marriage cert. - 5, Hillgrove Lane - there is a Mary KEPPLE, aged 48, widow, and a Katey KEPPLE aged 8; I'm pretty sure that these two must be his recently widowed mother and his young sister.
And Annie, I barked up the wrong tree with that Mallow KEPPLE family for a while before I realised that that could not be the correct William Jonas KEPPLE I was after.
So, Ken, the fact that you mention about initials being used for people in institutions in the 1911 census comes into play, surely. One can only guess at one of the "W Ks" being the man I'm after, but if one had to put one's money on it, then I would definitely plump for the one on Spike Island. Could one find out more details about which regiment was there in 1911, maybe...?
Regards, keith
K