Don't be afraid to ask questions. This is all new too you and there's lots of information posted very quickly which will probably take a while to make sense for you.
R.D.C meaning? 6a - 19B - are these cottage numbers? What would the office be hired for?R.D.C. is the Rural District Council which I mentioned earlier
'Office' is any sort of outbuilding- barn, stable, piggery, etc.
6a & 19Ba are the property numbers for valuations. Starting from Griffith's Valuation (mid-1800s) and continuing until c1930 the valuation records are online and document a property showing tenant & their landlord, description (house, etc.), acreage, annual rent & changes in occupier. These numbers will also appear on valuation maps- see here:
http://www.askaboutireland.ie/griffith-valuation/McKEEVER Elizabeth John McKEEVER Elizabeth McKEEVER Shanlongford Aghadowey Coleraine Londonderry 1851 - John & Betty McKeever md 1842, no return of a daur Elizabeth. Elizabeth born June 1851 1921 - Agents, Ballycrum, Limavady, Co LondonderryIn 1921 Elizabeth McKeever made a pension application giving someone at Ballycrum, Limavady as contact. She stated her parents were John & Elizabeth McKeever of Shanlongford. The 1851 census was checked in Dublin (this was just before it was destroyed) and that census said John & Betty McKeever were married 1842 but no daughter Elizabeth listed in household. It would seem that Elizabeth either said she was born June 1851 or this was proved otherwise.
John MCKEEVER - - Shanlongford Aghadowey Coleraine Londonderry Hired with Jack MCCURDY.At an unspecified date a John McKeever of Shanlongford made a pension application saying he was working for Jack McCurdy at the time of census (1851?). No indication if he was located in census or any other details.