So Bruce, let me paraphrase what you are saying & see if I've got it right:
CAPY is just a handy way of classifying cars & can be ignored when actually loading a car.
Ld. Lmt. indicates the actual weight of freight you can put in the car.
This is something that has puzzled me for probably 60 years, but I've never been motivated to actually go out & find the answer.
Thanks for the enlightenment! - Tom E.