Keith makes an excellent point, you might consider your checking tools before considering the plane to be out of square or out of flatness. I have a certified granite checking block and a precision straightedge (not the one I use as a winding stick, but another made for planes), outside of that I don't own precision checking squares. Precision squares meaning checking blocks for squareness, not brass or steel squares, double squares, etc which could easily be out of square by .001-.002" and I would never notice.
So to assume the plane is out of square is to assume the square is square, where the square can be out of square the plane square.
Even the table of Bridgeport mill is considered perfectly fine and acceptable if it's only out by a few thousands over the course of its travel. (A few is 2, not 5 or 10).
Bumbling forward into the unknown.