The inclusion of a child who participates in the spy adventure was intended to bring in the youth audience. It coincided with merchandising plans for a range of The Man from U.N.C.L.E. (1964) gear, ranging from toy guns to trench coats. This worked out well for 13-year-old Kurt Russell, who was later cast in a series of toy commercials for Mattel, which had developed its own line of spy toys under the banner of "Agent Zero M". A major impetus was that not only was The Man from U.N.C.L.E. inspired by the James Bond film series, but an impressive range of Bond toys had appeared and its sales had exploded. The U.N.C.L.E. and Mattel toys did as much business as the Bond merchandise.
The address on Solo's suitcase is 221 5th, NY NY, presumably 221 5th Av, near the Flatiron Building.