The black & white version of the printing instructions is from Avedon at Work. In The American West by Laura Wilson (2003 : 117 ; Amazon). Laura has a specific section on the printing process undertaken for the exhibition In The American West. She suggests that Avedon’s instructions were very general and that details for exposure were rather noted on test print (as seen above) by Ruedi Hofmann, Avedon’s studio manager :

The difficult and time-consuming process ok making these prints began in the basement darkroom of the Avedon studio in New York. Ruedi and David [Liittscwager] started with a set of 16-by-20 inch prints. Dick rejected them all. He felt that the tone was heavy; they were too black and had too much contrast. In reprinting, Dick’s directions were rarely technical. He would say simply, “Make the person more gentle,” or “Give the face more tension” This unconventional advice forced Ruedi and David to try to Understand the emotional content that Dick sought in each portrait. […] On test prints, Ruedi recorded the necessary manipulations with a red grease pencil. The exposure times, plus or minus, were in seconds to indicate where to darken or lighten an eyelid, or a nose, ot the wrinkle on a forehead.” (p. 114-117)

Laura Wilson was Richard Avedon’s assistant for six years (Wikipedia).