The single-piece video is a very detailed demonstration on how to create a single-piece coffin blanket. It clearly shows how the design is scalable to the required finished size.
A common requirement these days is for flowers to be shared after the funeral so by creating the coffin blanket in modules, usually three or four, the flowers can be taken away by different family members, left on the grave or used to decorate a table at the wake.
This video clearly shows what the three separate modules look like and how they fit together to create one seamless arrangement for the top of the coffin.