meanwhile, OED2 has the earliest citation for plunderbund dated 1914; note that it is only attributed to a publication and not an individual:

1914 Voice of People (New Orleans) 8 Jan. 1/1 The whole force of the Texan plunderbund.. are howling at the heels of the dauntless army of workers.

now in 1914 Adlai would have been, what, fourteen years old? and then he saved his coinage for just the right occasion, 34 years later -- all the while others were using it now and then?

something is amiss here. someone suggested to me that perhaps it was Adlai Stevenson, Sr. who coined it, but that seems to be a frivolous notion; the Stevenson biography clearly attributes it to Adlai II in 1948. it seems more likely that the word was still little heard after 34 years; and with Adlai's penchant for using the odd sesquipedalian word, somewhere along the line an assumption was made.

ofttimes the lexicographer gets caught up in this sort of detective work.

(I'd be happy to see any new or better information on the origins of plunderbund. : )

NB: I am not a real lexicographer; I only play one on the internet.