Rear Brake Caliper Differences

[DPDISXR4Ti]

Does anyone know what the actual differences are for the rear calipers before and after the listed 7/16/00 date? I come up with this date from car-parts.com, where it listed different parts based on this build-date. I don't believe it's related to the aluminum calipers, as I don't think they arrived until model year 2003 on the Sport models.

Any details appreciated.

Brad