The house numbers that appear in the censuses were generally the enumerator’s own private numbering system, and changed from census to census. They do not relate to any postal number that the property may have today. Until pretty recently, your name and your townland was all that was required to get a letter delivered. The postman and most residents would know where everyone lived. No further identification was required.
The Valuation Revision records for Ballindoalty are on the PRONI website. They list Edward Hughes as renting plot 11a. He is deleted in 1906 (suggesting he had died) and replaced by Jane, who in turn is replaced by James and then back to Jane in 1911. She remains the occupant through to 1929 when that series of records finishes. They are noted that she bought the freehold in 1928 under the Land Act (ie with a government backed mortgage).
https://www.nidirect.gov.uk/services/searching-valuation-revision-books
The Griffiths Valuation site has a map which shows you where plot 11a was/is. There’s an 1870s map and if you use the slider bar in the top right hand corner of the maps screen, you can overlay a modern map. Plot 11a was at the end of a dead end lane off the modern Killowen Rd, between Killowen and Lisnacree. There was a group of houses there. (Google Earth can show you what’s there today). The lane is about half a mile east of the Church of the Sacred Heart and runs south towards Carlingford Lough.
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
Edward Hughes appears to have died in Liverpool. Probate abstract:
Administration of the Estate of Edward Hughes late of Ballindoalty County Down Farmer who died 27 July 1905 at Liverpool granted at Belfast to Jane Hughes the Widow.
Jane appears to have died in 1943.
Hughes Jane of Ballindoalty Killowen county Down widow died 25 April 1943 Administration Belfast 15 September to Edward Hughes farmer. Effects £300 5s.
The term "Administration" means the person was intestate. So didn't leave a will. Both probate files should be in PRONI in paper format. They are free to view if you go in person.
