I posted this elsewhere but it may help here:
Just an update to this post… we now have a team for Prospects instead of a prospect board and each prospect has their own project created from a template that can be moved to our Client Work Team when necessary. We have the separate board and the old “prospect info task” is now the Client Info task within the prospects project. This is multihomed between the project and the [INFO] Current Clients board which lists the stages of our clients from prospect to closed. In this way, the Client Info task remains part of the Prospect when they convert to client and it never leaves the [INFO] Current Client board either. We just move it between the phases