Unit Preferences named year-person and month-person

[Kip Cole via CLDR-Users]

In the supplemental data for unit preferences there is a reference to the unit names `year-person` and `month-person`:

  <unitPreferences category="duration" usage="person-age”>
    <unitPreference regions="001">year-person month-person</unitPreference>
  </unitPreferences>

But I cannot find a reference in the locale files of such a unit. Only `year` and `month`. These names don’t appear in
`validity/unit.xml` either.  

A scan of TR35 doesn’t turn up an additional references (beyond unit preferences) although the pending PR for 
unit conversions does contain `year-person` and `year-month`.

Am I missing a subtle interpretation of these two unit names?  All others I can find in `unitPreferences.xml`
match the unit names in the locale files.

Thanks, —Kip