I've found some pictures of the difference in display's between old and newer models.......I actually prefer my old style one! New one looks a little cheap!
I have had both styles and like you thought the extra petrol gauge segments would be more accurate. They're not. Records full for 110 miles then half the segments disappear to leave half full . I wondered if the extra segments might be for use on the GSA and they put the new clock on the GS to keep cost down