My method for lining up rows with sashing is as follows. I sew a long strip of sashing to the bottom of the first row. I iron that, then turn it to the wrong side. Using a ruler and pencil, I draw lines that extend the seams through that long row of bottom sashing. This creates "virtual" seam lines in the long sashing piece. I pin the second row to this long sashing strip, making sure to match seams in the second row with the virtual seam lines marked in the sashing. When sewing this seam, I ease as necessary to keep the pinned lines matching. I repeat this process as each row is added. It's a simple way to keep blocks lined up when you are using sashing without cornerstones. The pencil marks actually take the place of cornerstone seams.