The three texts are:
"Cantaboff" of course refers to "Cantab." and the author's recent graduation from Trinity College, Cambridge; "Sirine" was Nabokov's occasional French spelling for "Sirin", his early Russian pseudonym.
The only known previous appearance of these three texts had been within the second issue of a trilingual (German, French, English) brochure, Karussel — Carousal — Carrousel, published in Berlin in 1923 as the prospectus for "Karussel", a Russian theatre travelling to Berlin.
Stella de Does-Kohnhorst discovered a copy of this rare prospectus, gave it to the Nabokov family, and asked for and obtained their permission to publish the contributions by Nabokov.
There have been two ions, both designed by Bram de Does and published in 1987 by Spectatorpers in Aartswoud (the Netherlands). Both claim to be "limited" (to 100 copies of the first, and 150 of the second), but copies of both with "HC" in place of the number are known, suggesting larger numbers. The publisher's note to the first ion explains the reason for the two ions: a detailed "Introductory Note" by Dmitri Nabokov, the author's son, had arrived too late for inclusion in the first. Thus the first ion lacks this note; the second, which is in a larger format, includes it. The first ion — of which Michael Juliar has stated (without explanation) that "Thirty or so copies survive"  — is a paperback that was not offered for sale; the revised ion was made available in hardbound and paperback versions.