interesting question. I typed a longer reply, but lost it. Oh well, anyway, as to your question about the consistency of language among all the styles, Yang and otherwise, there isn't any. "Jin bu" and "shang bu" are both translated as "step forward", even in the same texts. This may be a matter of convention or it may actually be a matter of individual technique.
In terms of the movements, almost everyone does "step forward, grasp bird's tail", "step forward, parry, punch," and "step forward/up, seven stars" differently. Translating "shang bu qi xing" as "Step Up, Seven Stars" makes a little more sense. But, one also sees "shang bu, lan que wei" or "shang bu chui", etc. very often. I'm not sure if there's always consistency in tcc styles. At least, I'm not sure that the language illustrates or represents the actual distinctions in the movements.
In bagua theory, "shang bu" is "the Upper Step"; and the rear foot steps past the front foot. OTOH, in "the Advance Step" (jin bu), the front foot moves to the front.
This makes sense, but I'm not sure if it's consistent with the vocabulary used in the tcc forms. It does accord with the idea about Step Up, Seven Stars. But, as for the rest of the form/forms, ymmv.