DTV12 — Why not fractional months?

In clause 9.3, in the entry for 'duration value equals number times duration value', we find the Necessity:

Necessity: If duration value1 is a nominal duration value and the number is fractional then the time unit of each atomic duration value of the duration value is not ‘month’ and the fractional part of the number is ¼, ½, 2/4, or ¾.

This Necessity, the four Necessities that follow, and the Note that follows them, are constraints on the number part of a nominal duration value. They are not necessities about scalar multiplication. At best all of this should be moved to 9.2.3.

This necessity, however, is unnecessarily restrictive, and appears to be utterly inappropriate. 1/3 year is 4 months, 1/6 year is 2 months, and 1/12 year is 1 month, and their multiples are multiples of months, but they are apparently "not common in business usage". Moreover, in estimating a contract, why couldn’t one multiply a standard duration estimate stated in months by 1.2 to allow for some delaying factor? And similarly, if we average seven durations stated in years, the multiplier is 1/7. Business analytics will generate fractional multiples of months and years. Why should DTV disallow them?

The Note provides the underlying motivation:

Note: This specification defines only the fractional nominal duration values ¼ year, ½ year, 2/4 year, and ¾ year because these are in common business use and they equal an integral number of months. This specification does not support any fractional 'month' duration values

because such fractions are not in common use [which is false] and because they are not equal to an integral number of years or days [which is the real reason].

Integral number of months or years are not equal to an integral number of days, either. But, per 9.2.3, they correspond to time sets (in days), while a fractional number of either does not. How important is this?

The RTF agrees that the cited Necessity is an unnecessary constraint. It is deleted, and the subsequent Note is revised.