I think it’s a metaphysical fact that all borders are blurry if you look closely enough in the right places.There are times when non-CHOSSA are treated similarly to CHOSSA. I've seen pages from a 19th century biology text claiming that the Irish are not really white. Groucho Marx was once not allowed to use a hotel swimming pool because he was Jewish. (He asked if his son could wade up to his waist because his son was only half Jewish.) Rebecca Stevens is not CHOSSA, but she still experiences lots of racism in Switzerland, and writes eloquently about it.

Trying to answer these kinds of questions once and for all is like trying to decide whether a tomato is a fruit or a vegetable. It's not a question of what's real, it's what is important. The border you're talking about is certainly very important, for all the reasons you give here, and the fact that there will always be borderline cases doesn't change that. That's true of all borders between anything and anything else.

Let me add another reason why I think the line you are drawing is important. Only CHOSSA have to deal with the problem of Being Rich While Black. Racist Americans seem to have relatively little problem with Irish or Italians becoming rich. A rich Black person however is considered to be an affront and an insult to some white people. I know of no cases of white mobs doing to Irish or Italians what was done to black people at Tulsa, Rosewood etc. I think this is one of the main reasons that Black people have not been able to accumulate as much generational wealth as immigrant groups have. Once they get it, White mobs destroy it.