"it took another generation or so for the drink to assume its classic name and form, during which time it tried on several identities. Here it's a D&S...there a Little Club No. 1 (the Little Club being a rather swank sort of joint on East Fifty-fifth Street much haunted by showbiz types); at USAF Officers' Clubs in Thailand and the Republic of Viet-Nam, it's a Mig-21, while in the upper Midwest it's a Knucklehead."
This passage describes how the drink went through different names and identities before settling on its current one. It was initially called "it" or something else, then became known as "D&S," "Little Club No. 1," "Mig-21," and finally "Knucklehead."