After reading all of this I have an observation. When cutting out the squares on the corners shouldn't you ADD the half inch seam allowances TO THE SHEET instead of adding it to the part you are cutting off??? You want the seam allowances on the part of the sheet you are keeping wouldn't you??? or am I just not reading it right???
For instance, somewhere you mentioned for a queen size bed to cut a 15 1/2square. Shouldn't it be a 14 1/2 inch square??? Leaving a 1/2 inch seam allowance on either side of the square??