I think the issue is that a lot of ppl think of samurai as these special elite mythical forces. Like whether Yasuke was a full-fledged Samurai in the traditional sense or not shouldn't really matter. As mentioned, a lot of documents from the time have been lost. If Nobunaga gave him the title of samurai and the benefits/ responsibilities that came with it, then it really shouldn't matter how that came to be or how much of a samurai he was.