Whenever you see '1/4" seam' or 'scant 1/4" seam', it really means the same thing -- the seam allowance that will give you the correct size block with the machine and thread you are using. I think the terminology used is just a matter of preference. Whether a pattern says 1/4" seam or scant 1/4" seam, it's always good to do a test piece to see if your block/unit is the size it is supposed to be. If it's not, then you have to adjust the seam allowance.