Our contract states those individuals are acting as agents for the company.
We have converted most of our depositors to plastic bags, write or wrong it eliminates the issue of picking up bags. We document the bag number and the customer keeps the portion they tear off.
I would tend to agree with Jokerman. My issue would be having the signed contract and the information is no longer accurate, if there is a lot of turnover with the individuals picking up the bags they may want to just provide you with notification when something changes so that it can be filed with the contract.
Do what you can, with what you have, where you are.