As extensive as the documentation of the dining room buffet windows may be, there is no documented resolution to the questions of their design, fabrication and installation. This lack of documented resolution reminds us that telephones were in use at the turn of the century, and this (and so many other) details of finishing the Martin House may have been resolved when Darwin Martin picked up the phone and called his architect - conversations that Wright may have come to dread and, unfortunately for us, are utterly lost to history.
In light of this incomplete record, I will attempt a relatively sober interpretation, based on the available evidence:
Of those who may have had a hand in the design of the windows - Wright's studio or Giannini and Hilgart - I think the design can most likely be credited to Giannini (or Blanche Ostertag, the probable designer of the wisteria fireplace mosaic for the firm of Giannini and Hilgart). The design has none of the hallmarks of Wright's work in art glass: chiefly, a more abstract, geometric and symmetrical rendering of natural forms. Also, the letters suggest that the design of this frieze was soon out of Wright's hands and he then turned to the uphill battle of trying to control the work of others (indicated by his occasional admissions of conflict with Giannini).
Of those who may have executed this design and fabricated the windows - Linden Glass Co. or Giannini and Hilgart - my money again is on Giannini and Hilgart. The more conventional lead caming and painterly use of irregular glass seems in keeping with their known work in similar media. However, another plausible possibility is that some local (Buffalo) stained glass craftsman (Martin's "glass man who never heard of Wright") built the windows based on Giannini and Hilgart's drawing, which Martin - apparently determined to take charge of the languishing project - may have obtained. However, if there's truth in Wright's claim that Giannini and Hilgart lost the drawing (Wright's drawing? their own drawing?), more doubt is cast on this last supposition.
The letters concerning the dining room buffet panels do tell us one thing for sure: their design and execution was a protracted process. This easily explains why we see plate glass in the three window openings in the Fuermann photo of 1907. Essentially, Martin and Wright were so busy hashing-out many other details and open issues of finishing and furnishing the house that some projects ended up simmering on the back burner for years. One can easily imagine (NB docents: this is in the realm of speculation) that the extant art glass frieze of tree trunks and branches was not installed until 1910 or later.
The most timely question of whether the extant panels will be removed and replaced with plate glass during our interior restoration is still an open question. We have clear evidence that a temporary enclosure of plate glass was installed circa 1905 (when the Martins moved into the house), but the letters clearly indicate that Wright intended for these apertures to have some sort of art glass by the time the house was complete (whether he was capable of fulfilling that intention or not).