I would like to ask on the top of seriosity. Please, read it twice: How could "taoism or buddhism" have had "separate origins" and still stayed "the same thing"!?
I take the time to comment only upon the above aspect of your post, Dharmaatmaa.
One essential of maintaining separate origins of thought and its "purity" is to create a wall or barrier to intrusion from outside ideas. In the course of history the natural barriers of mountains, seas, and deserts have provided such isolation.
While trade routes may allow for a limited exchange of ideas between isolated groups, the overall effect of those ideas upon a different society that is in isolation will be somewhat limited short of establishing a colony, a school, a major transport route or an outright invasion.
One may examine the customs of peoples within the borders of ones own nation and see that differences of ideals and language usage exist. These differences, however subtle, becomes especially noticeable where there exists limited travel and/or contact involved for whatever reason(s).
One may look to the differences in Buddhism as practiced in various countries and see both similarities and stark contrast, the same can be said for the various "flavors" of Christianity as well. There is an inherent resistance, or inertia, to change and the introduction and adoption of new ideas that can be seen around and about us in our daily lives today.
How much more so would this inertia and isolation have effected the world in as little as 100 years ago let alone 1000 or more years in the past?