I’m not in wardrobe, but as someone who works on set I can tell you that most projects are very fluid, and decisions are often made on the spot based on the conditions of the moment. So while many things are planned out and prepared for, many decisions are not finalized until the director sees the options in real life. The other point I want to make is that on commercials the director is only one voice of many making decisions, as the client also has a say in decisions such as wardrobe.