Broadly speaking, given that IBNR in reporting year only consists of IBNER, in accident year it consists of pure IBNR & IBNER, and underwriting year consists of IBNR, IBNER & unexpired risks, would this mean that the ultimate claims produced in the triangles will be such that UWY > AY > RY?
No: When you do a triangulation, you're always going to end up with the same ultimates regardless of the cohort used (think about it, if I gave you a triangle of numbers but didn't tell you the cohort used, and asked you to do a BCL on it, you'd give me the same answer!). BUT what those ultimates represent (in terms of reserve components) will differ depending on the cohort. There are past questions about this, and other threads in this forum covering the same topic.