The curse of a researcher - Curiosity - was piqued on seeing over time several footnote references to an unpublished article by Gene Smith,
The Era of 'Gro-mgon 'Phags-pa and the Apogee of Sa-skya power:
a Preliminary Report. (1962)
An initial enquiry email to TBRC produced no result - they did not have the piece.
Further communication with staff at University of Washington Library (Seattle) eventually unearthed a listing of a cache of papers on Tibetan Studies written 1959-1971 -
with thanks to Martha E. Pearson for her adept assistance.
UoW Library has now put the listing online as a PDF.
(curiously, the Gene Smith 1962 article is not listed on the PDF,
although UoW does have the article)
Hard copies of the papers and articles can be ordered from UoW Library,
through this link.