Hi Mary,
Welcome to RootsChat.
Did both those addresses come from the birth registration record?
In 1911, 4 North Brunswick Street appears to be occupied by Matron, nurses and Sisters of Charity so seems to be a hospital, perhaps within a convent. Is the address of the parents the same as the place of birth?
I haven't yet found 4 Marlborough Street on the 1911, but parts of the street are in Mountjoy district and parts in North Dock so perhaps number 4 is in yet another district.
There does seem to be a possible marriage registration in 1905q4 with the same reference for a Christina Kelly and a James Byrne in Dublin North (I think that both the addresses that you have given would fall within Dublin North and the Pro Cathedral is in Marlborough Street so a likely venue).
What makes you think that this would be the right date for the marriage?