Why is CLDR missing past/future unit data for certain locales?

[seaneagan]

These locales (there may be others):

no
in
iw
zh_CN
zh_HK
zh_MO
zh_SG
zh_TW

do not have cldr data for past/future units, example:

http://i18ndata.appspot.com/cldr/tags/provisional/main/no/units?action=browse&depth=-1

For now, we are defaulting to the plain units for these.