I’m curious on whether these were spur of the moment names or if there was a system in place that determined a titles name. Eg. Was General of Vehement Might a position in existence before and after Lu Bu’s appointment?
This post does not answer the question, but addresses some of the underlying assumptions in the question.
Do you you mean specific rather than elaborate? In Chinese the syllables and characters required to get across the idea of vehement might and western garden are not any more elaborate than saying "big" or "first" western army. For example xiyuanzhun for Army of the Western Garden isn't really any more elaborate in Chinese than if you called it daxizhun or Big Western Army. It's also not really any more elaborate than some US military naming conventions like 1st Stryker Brigade Combat Team or Command Sargent Major for example.