The fourth part of the eligibility and entitlement process is to check if reassessment is required, and if required, to run reassessment. The purpose of case reassessment is to compare the outputs of a retrospective eligibility and entitlement with the outputs of a previous eligibility and entitlement over the same period of time. This comparison detects differences between these outputs so that the necessary over/under payments or over/under billings are created. An under or over payment occurs when a new decision is created for a period that overlaps with an existing decision or decisions that have already been processed for payment or billing and that new decision differs from the existing decision or decisions. An over or under billing is the same, only for a liability product instead of a benefit. To check if reassessment is required, the eligibility and entitlement engine compares the cover period from date of the new decision to the cover to date of the case. The cover to date of the case is the latest cover period to date for all ILIs. These ILIs are the output from the processed financial components. If the new decision from date is before the cover to date, reassessment must occur. The eligibility and entitlement engine then defines the reassessment period and determines if any under or over payments (under/over billings) exist by comparing the ILIs to financial data associated with the new financial components.