Seams in a backing:
It may be that a pieced backing that needs to be lined up 'exactly' with the top might be problematical? Especially if it has to go in 'the not usual' way?
For a backing, I was told to remove the selvages and to use at least a 1/2 inch seam. I don't remember if I was supposed to press the seam open or to the side for the backng.
What about seams that are twisted ? End A goes north - end B goes south?