My MDT is that way, GVWR is the sum of the axel wt ratings! most rigs over a DOT class 5 truck ARE that way, Only in light duty and some class 4 rigs is the sum greater than the actual.
Depending upon the state or canadian provence you are in, the sum or lower number may be the actual law. In Washington, non of them matter, it is how much you have a paid for license for. The minimum is the next highest ton at 1.5 times the tare. You can only buy registration tonnage tags by the ton. SO for the ops rig, a 6 or 8k license for the truck. He would be legal for one of those numbers, He could also buy a 10K plate, and be legal to that number too.
My 18200 navistar is licensed at 26K, been pulled over at just over 27K, no overwt tickets so far. As they give my 600 lbs per inch width of tire! WELL OVER that door sticker which is in my office! My now sold 05 dually, was licensed at 14K, no issues going thru scales either.
Not sure truly why the sum of the axels is greater than the gvwr.......probably as said, so idjiots can load it up incorrect, and still be under the warranty equal numbers.........
Marty