The Will was not legally executed. The fact is that a Will must be witnessed. Since the witness signatures pre-dated the testator's (i.e. your father), then there was nothing to witness when the so-called "witnesses" signed. Accordingly, the Will was not validly executed. Frankly based on these facts, while this may have been a simple misunderstanding, it may have also be indicative of something unsavory going on regarding his estate. You may want to consult with a probate attorney on this.