Jim, nice observation. I don't know if I ever thought about it. I have both types too. They made these for a long time, not surprising that the mold would be changed from time to time. Borland ID'd two types of diamond molds in his list, but just one hub mold.

The two chips below are the same size, but;
¶ orange chip -- rectangle hubs (90 degree corners) -- the two incised circles are 24 mm and 33 mm.
¶ yellow chip -- trapezoid hubs -- the two circles are 26 mm and 35 mm.

Robert