I suspect a significant factor here with regard to SAR ops will turn out to be R116's crew's familiarity with the type of mission they were scrambled to. Those aircraft on the west coast are a lot more active than those on the east - not surprisingly. The busiest is R115 at Shannon, which in 2014 completed 310 missions whilst R118 at Sligo wasn't far behind on 277. In contrast R117 at Waterford completed 187 and R116 at Dublin just 130 - the same (131) as in 2003, when - and this is interesting - just 13 missions were at night, compared to 57 for Shannon. And from R116's Dublin base, it's likely few of those were off the much less familiar and hostile west coast.
So we have a picture here whereby R116 may only have flown 3 or 4 night missions over to the west coast - and off it - in the last year. Which fits with their stated lack of familiarity with Blacksod. Perhaps someone with more knowledge can provide a more accurate estimate?
Of course this means flight planning needed to be even more carefully done, and charts and route guides appropriately clear, for rare and challenging missions to be flown safely.
Does anyone know why R115 from Shannon was not available to provide top cover that night? They would doubtless have been far more familiar with Blacksod and its approach.