I just love these "We invented X-Y-Z before you eeevil Whites did" stories. They're usually about cultures that did absolutely nothing with the knowledge. The Chinese may have landed in North America before the Europeans did; but so what? They never exploited that knowledge. The Africans may indeed have had knowledge of advanced mathematics. But what came of it? Nothing; they are barely Iron Age societies. What technology they have came from the outside. The Arabs go one and on about inventing the zero; but their level of technology (a tangible expression of their alleged math skills) is a zero. They invent nothing.
Having a bit of knowledge isn't quite so important as using that knowledge.
One of the major problems with any such claims is analogous to the discovery of *the planet* Pluto. Clyde Tombaugh found it in his systematic search, and had been hired to search by Lowell Observatory. Lowell O was founded by Percival Lowell, who had been dead for a number of years by the time Tombaugh started working there. In order to increase the baseline of observations to calculate the orbit of the newfound planet, prediscovery observations were searched for, and one was found on a plate exposed by -- ta dah! -- Percival Lowell, who had at the time been looking for his Planet X.
Another major problem is that discoveries are made by individuals or small groups working together (or working in competition). Credit doesn't go to whatever ethnic group produced the discoverer(s); and as you said, cultures which don't put any value on discoveries don't get any benefit.
Or at least, don't get any benefit until they're conquered by one that does. ;')