Exactly. While tube specs are not published to the general public, they are known to the builder. I'm sure that loading is also well known. So tube-and-joint carbon bikes are designed in the same general way that a metal bike is designed. If it is designed and not just built by rule of thumb. The huge advantage that this type of carbon construction has is that stiffness at the joints can be increased after testing. Thus a builder can get it just right and with experience, not need the testing and fiber adds. Can't do that with metal. It is not yield strength that's an issue with quality construction, it's stiffness. None of these joints come anywhere near yield strength. Cyfac probably adds the Kevlar not to increase stiffness or yield strength under normal loading, but to increase the chance of the joint surviving a catastrophic stress, such as in an accident. This is common practice in the marine industry.