2.1.1099 Part 4 Section 3.17.7.345, XIRR

a.   The standard specifies that an iterative technique is used for the implementation of this function.

Office does not require an iterative technique to be used.

b.   The standard states that if any date in argument dates is out of range for the current date base value, #NUM! is returned.

In Office, if any date in argument dates is out of range for the current date base value, #VALUE! is returned.

c.   The standard does not define any restriction that argument values must contain one positive and one negative value.

In Office, if argument values do not contain at least one positive and one negative value, #NUM! is returned.

d.   The standard states that if any date in argument dates precedes the start date, #NUM! is returned.

In Office, dates in the argument dates can precede the start date.