Today's Random Question: Actor Assistants

When you read the credits for a film, lead actors very often have assistants listed. Looking through some Playbills, at the tiny font text between Who's Who and the union logos. I never see "Assistant to [Lead Actor]". Do Broadway stars of a certain caliber, i.e., Lupone, Ebersole, Close, et al, ever have assistants written into their contracts, or do their existing assistants just handle day-to-day errands and what not?

Many actors have assistants, who work for them on an ongoing basis and whom they pay directly. I've never heard of a production that individually staffed an assistant for an actor for the run of the show.