When we have an index lease update, the system does not have the functionality to allow you to apply the change retrospectively (it does not do the calculation for a catchup adjustment for the prior periods), instead we have to manually calculate what that prior period adjustment would have been recorded in the periods prior to the open month and add a payment line to reflect those past changes.

The current functionality in the system only works if you receive the new rate before the old rate expires.

Our index changes are typically retrospective as we seldomly receive the new index rate prior to the old index rate expiring.