They might have added all the rotations of both wheels of both rovers together for the rotation number.

Another consideration is one which should have been used.

Nothing should have been built to outlast anything else. Since it can't be repaired the estimated time of the first fatal failure should determine how well the other components are built. They should be built as light and inexpensively as possible. There's no sense in having a component which will outlast any other component.
By the time of the first fatal failure the rest of it should pretty well be junk, too.

Since your vehicle is designed to survive almost any breakdown, it makes sense to design components to last as long as is budgetarily possible. It would be foolish even so to spend the money to build a transmission designed to last 1,000,000 miles if very few of them are driven more than 200,000 miles, for instance.

I think that's one of the challenges of building something like a spacecraft.