If you want access to a 1929 marriage, you won’t find it in PRONI. The relevant records are in GRONI. As has been mentioned already these will be on-line sometime in the next couple of months. In the meantime if you want a copy before that, contact GRONI. They will provide a copy for £15. (There may also be a search fee if you don’t have an exact date).
Regarding the 1911 census entry, the number 40 is not the postal address. It’s the enumerator’s private numbering system which he used to ensure he went to every property, including those which were shared or had no street number. If you want to see the postal address, click on “household return (form A)” and you’ll see that the postal address for that property was no 20. So no amendment is required to the census information. It’s correct.