Charlie Weiss was on Phil Perry's podcast recently, and talked about the first time he was the playcaller for Parcells (in New York I think he said?). He said he was the playcaller for a season, but publicly Parcells said it was someone else. It was a way of getting Weiss experience doing it without having the scrutiny on him every time a playcall goes wrong.
For those wondering what the advantage of not naming the playcaller is, it's not about game day advantage. It could be about protecting a young coach from the ****storm that tends to ensue until he can get his feet wet a little.