So they were basically removable “Post it” stickies representing units of time spent on the customer’s case represented by the specific sheet, which were collected in the customer’s file in the end? Do you remember how you kept track of who did the specific unit of work? I.e. did each employee have their own sheet for each customer to collect their stickies on? Was there any color coding, any information written on the stickies?

I’m interested in those paper based techniques because I learned over the years that physical representation of abstract things helps a lot of people keeping a general overview in projects.