I understand your point, but this isn't a local anomaly. We're talking about the cut and dry first cotton mill in America. If this was the first Ma and Pop's Hoagie shop, well then yes that would be in a local context, but this is a national to international matter of relevance. This is not a regional interest topic. The BCM is extremely notable and worth mentioning in this article. If you want to subdivide the article into pieces based on regionality, then let's create a Cotton Mills in America article and put the BCM at the top of the list.

As far as Slater's history is concerned, there was a progression between animal and water powered production. I don't have the information on any other animal powered production facilities, but you mention that you found two or three references to animal power in 1400. Why not add them? They're part of history. Perhaps the framework of your date titling system in Cotton Mill is rubbish and needs to be changed, because no matter what stance we take here, the article is clearly missing information that could be incorporated. Providing only the information there allows people to make incorrect inferences.

In the context of Cotton Mill, are we to add an animal-powered category, or are we going to omit that from history? The Water powered section is nice, but we should show a greater view of earlier mills, both in America and across the seas. Don't hold back now, you appear to have more information about other mills. Add that information, please!