Has it happened that slack was taken up or a t/o roll started with no one in the glider AND a wing runner signaling to do so? I'm guessing so.

In any case, when in Rome, do as the Romans! In other words, if you are new to an operation, brief.

“The pilot of the towing aircraft and the glider have agreed upon a
general course of action, including takeoff and release signals,
airspeeds, and emergency procedures for each pilot.”