" So, I put forth this question: can anyone prove that Crossdressing isn't a predecessor to transgenderism and a valid ingredient in Transgenderism since inception?"
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Labels usually are not adequate to properly describe someone as the label will likely have different meanings to different people. Labels also create a sort of "box" that can be limiting.
What would "prove that crossdressing isn't a predecessor to transgenderism"? If the label transgender is a term that includes crossdressing then, crossdressing is a part of transgenderism and does not "lead" to it.