I just cut the threads on the one Fun n Done. I was going to use sashing, and stitching the sashing would cover the threads in the blocks..
I got tired of burning fingers trying to turn the back over so I just squared all the blocks, zigzagged them together then added sashing top and bottom. Been on the bed for over 3 years and washed. No problem except too much cat hair.
The Queen of Stitching has another method for the backs and sashing. It works pretty well. She has a web site and videos of how to.