Diplomatic cargo...sounds very ominous, doesn't it? Conspiracy theories abounding, secret government agents on board, crew can't know what they're carrying and all that garbage?
The majority of the "diplomatic" cargo on these flights is letters from wives, girlfriends, college campuses, and credit card companies...every day US mail enroute to government employees, troops, contractors, back and forth. Vehicles get carried...straight forward, simple vehicles. Generators. Mops. Paint. Whatever is needed gets carried, very simply put. Nothing sinister here, nor was there any top secret, can't-tell-the-crew-how-much-it-weighs cargo involved. Didn't happen.
The weight of the cargo is and was known, and it's already been verified for this flight. As it's not an issue, why do you keep bringing it up? The weight was not a factor. The performance calculations were correct. The cargo was secured. It was balanced correctly. Enough already.