I looked up the 1911 census, and can see what you mean. I could only find a handful of households in New Zealand Rd.
The census does give Enumerators' book images - the links are at the top of the page when you view an original image. They cover: List / Cover / Details / Totals / Description . They are all free to view.
The 'Description' tab for the few New Zealand addresses gives details of the enumerator's 'patch'. If you knew the area it would probably make more sense, but it does say he covers only 287-291 New Zealand Road (he then goes on to St James's St). I'm assuming this means the rest of the road is covered by a different enumerator, whose writing has been mistranscribed, and therefore difficult to find. The only hope, I expect, would be to find someone else from that road (maybe from a directory) with a more searchable name than Williams!
Good luck!