2.1.944 Part 4 Section 22.214.171.124, CUMIPMT
a. The standard does not define the return value of the CUMIPMT formula when end_period is greater than nper.
Excel returns a value of #NUM! when end_period is greater than nper.
b. The standard states that start-period and end-period are numbers.
Excel truncates start-period and end-period to integers.