16550 Ivory Explorer 2 bezel question

HiIt is generally accepted that the Explorer 2 ref 16550 came with a bezel with a fat font. The "2"s in particular have a flattened and thicker look to the bezel on the later 16570 model. I have a rail dial 16550 from 1987 with the 16570 type bezel. At first I did not think this was original until I bought a Rolex catalogue from that year and it clearly shows the 16550 with a white dial, white gold hour dots and hands and the 16570 bezel. Was this done as a rolling change?ThanksGF