IBNR and Plan Design Changes

Say we have a 36 x 36 month claim lag triangle through November 2014, and there was a plan design change effective January 1, 2014 resulting in a .95 impact to claims going forward. Why exactly would we want to adjust claims prior to January 1, 2014 to today's level (.95 impact), since if a claim was incurred prior to January 2014, it should be paid under the plan provisions prior to the plan design change, regardless if the run-out carries into 2014? So, if all claims prior to January 2014 are multiplied by the .95 factor, wouldn't we be underestimating the IBNR for those months prior to January 2014 that are not fully complete?

IBNR and Plan Design Changes