Thanks again heywood and josey.
The nine living children were all known to my aunt - Maggie, Mick, Billy, Nell, Jack, Jim, Bid, Joe and Ted. The 1901 and 1911 censuses (and the civil birth records we found) seem to confirm these names.
Yes, the marriage was 3 Feb 1894 (civil record). My Irish Genealogy searches only turned up 10 births total between 1893 and 1920 that match this couple. (I always check for a possible illegitimate birth before the marriage, and although Ted, b. 1912, was the youngest I also checked for the possibility of an even younger child who didn't survive).
I've attached a screenshot of what I've put on Ancestry.co.uk for this family for aclearer overview of what we have. I've included the grandparents to show that the naming of the first few children doesn't quite match the RC tradition.
Regarding the obscured number on the 1911 census, I noticed that the enumerator puts the loop of his 9 rather low. So could the obscured number be a 9? If that's the case then only one child died before the 1911 census and we have him.
I'd agree that the 1906-1909 looks like the best place to search for missing births, if there are any. If there were twins at any stage I'd have expected to find them together in the civil births - is that a correct assumption ?
Still births and miscarriages (including possible twins of those who survived) could perhaps, just possibly, also account for the original family story that there were 17 children ? But there wouldhave to have been a lot of them.