There are also three duads, seven tetrads, one nonad and 31 single items relating to monasteries at the start of the collection.
It does appear to be particularly popular in the literatures of Celtic-speaking areas, one notable other example being the later Welsh collection Trioedd Ynys Prydein ("Triads of the Isle of Britain").
Although triads can be pointed out in both Irish and (again later) Welsh law texts, they are the rule in neither as other numerical forms are usually preferred.
Fergus Kelly concludes that "[t]he case for a special Celtic cult of threeness is unproven, as is the attempt by Meyer and other scholars to establish a biblical origin.
He based his text on six manuscripts (YBL, BB, Uí Maine, Great Book of Lecan, 23 N 10 and H 1.15) and was aware of another three (23 N 27, Rylands copy and Kilbride).