This raises an excellent point: I have never seen a set of instructions for squaring a quilt that has points on the edges. And I have never seen a discussion of how to square a quilt without the blocks being "reduced".
Most of the instructons I have watched online just use a seam to make the first trim, then use that side to make the square cut for the next side. Obviously this can result in cutting off points or cutting block sides at an angle.
While this points up the necessity for accuracy when completing designs so that the squaring is not going to mess up your edge blocks, I wonder why, if we are not submitting the quilt to a panel of judges at a show, we square up at all. If the quilt is a bit off square but is just a cuddle quilt, does it matter??
The best preventive I would think is to put a border on first? Small irregularities in the border would not be obvious.
Or should you block (steam and press into square) the quilt to make it square?