Hi Jerrid, welcome to the forum. I am going to do my best to follow you here. You're saying you feel you may have a heretofore unknown small date 1959-D variety, correct? This is based on measuring the width of the 9s as compared to your 1955 and 1956 NGC graded coins, correct? Or have I already made a misstep? If I have, I should mention that you need to be comparing the design for the same year. There are sometimes minor variances in design from year to year, so that would not make this a small date just because it's smaller than a 55 or 56. Furthermore, variance in size of devices within the same year can sometimes be because of either a doubled die or die polishing, which would result in larger or smaller devices than normal respectively. Overpolishing would need to be ruled out in this case after you compare your maybe-small-dates to a control coin.