The current logic in Mambu for index rate linked products is to start the index rate on the disbursement date:
For certain products, the rate for the first instalment will already be captured in the legal documentation agreed with the client on the approval date. The rate provided to the customer will be an all-in rate (including any margin/spread built) and this will be on legal documentation that will be electronically sent to the customer, who will have x number of days to sign these documents.
If the index rate is changed within the given timeframe, the customer may still be within the allowed timeframe to return the documentation but have the rate changed (at disbursement), although the legal documentation alludes to a previous rate.
This may cause legal loan documentation to be invalidated/open to challenge.