whole nine montagnards

[Mullins, Bill]

Supposedly, the nine tribes of Montagnards has something to do with the
phrase "whole nine yards".  But this, apparently authoritative, book:

_Minority Groups in the Republic of Vietnam_, published 1966 by the U.S.
Army, lists 18 Montagnard tribal groups (see the bottom of page v in the
preface; the fifth page in the PDF file).  (online at:
http://www.vietnam.ttu.edu/star/images/137/1370507001a.pdf ).

So, should the phrase really be "the whole 18 yards?"