Do not over think this -- nothing changes from the original engagement. Clients have responsibilities after the return is completed -- it is their information and they have record retention requirements at a minimum - do not give credit for what they do not know or understand. Ignorance of the regulations is not an acceptable excuse.
Think of it this way -- you purchase the a new washer and dryer - with all the latest technology -- even connects to your wifi -- the sales person goes over how to use it and the warranty (what you need to do to maintain it), some time later it is delivered and installed. Do you remember everything you learned at the time of purchase? The installer goes back over everything to ensure you understand and asks for questions. Nothing changes. The installer asks you to sign a receipt that they have delivered, installed, made sure it was working and went over everything again with you. Same process, simply put it is customer service.