I think we're seeing 4 levels on a lot of our offensive calls. First, the coach to the field, and the package of players sent in. At that point, the selection of the play is one of maybe 3 options. Each needs to be called in sequence, then they go to the line. At the line, the QB moves his pieces on the field to gauge reaction from the defense, and their locations at that point. Then he may check into the second or third option. When he does, the center calls out the signals for the blocking assignments based on what he sees across from him. At that time, the QB starts the sequence of the play in motion.
In some cases, because of the personnel on the field, the QB needs to take the lead in the huddle to call out some personal assignments on plays, if the player package isn't the group that normally practiced this play together. This usually happens with a receiver, TE, or RB.
It's not nearly as complicated as it sounds, but it takes time to disseminate the information, and if the coach calling the signals believes his QB should have more options, there may even be some verbal statements of how the play should be modified as to how it's been practiced. I used to do that all the time, using rotational players into the game as couriers, to give those directions to my QBs and even some other players as well. A quick way of addressing an issue you see without calling time out, or having to suffer through until your offense is on the sideline.
