An and example of a cumulative loss triangle.
CumulativeAutoBodilyInjuryTriangle
Rows pertain to accident years; and columns pertain to development years. For this triangle accident years range from 1974 to 1991 and development years range from 1 to 18.
Hayne, Roger M. (2003), "Measurement of Reserve Variability," Casualty Actuarial Society Forum, Fall 2003, pp. 141-172, http://www.casact.org/pubs/forum/03fforum/03ff141.pdf.