I think by now most of your concern is cleared. Let me add this. Ever profession has its terms coined from related early versions. This evolvement of technical terms depend on multitude of reasons. One of them is the ease of reference. Natural development of language has no set rules or terms to follow. People maek language and they themselves twist it in ways that seem practical for his purpose of communication. Tracing the history of an expresion is not always an easy task.
Back ground being so, about your partucular concern, waht I could say is that Tx has a clear tracable history and all other related x's are safe to be thought to have followed the lead.