Since this list does not include a common selection criteria, I'm not sure how a selection would be possible. To obtain a selection, it appears that you would need to either make a random choice, choose the entire list, or restrict the list in some fashion until one common criteria is available. People seem to use the term "atheism" as though it has a strong definition but I'm not sure how it would have any definition if "god" is not first defined.
Re-reading your post, I see that this nonsense about selection has nothing to do with your primary claim, which is this:
It makes no sense to declare "There is no god," unless the term "god" is well-defined.
And, there is something to be said for this. I wouldn't have an opinion on whether any numbers are flurbles, absent a definition of flurble.
On the other hand, of course, atheism does not occur in a vacuum. Rather, it occurs in a cultural context. The overt atheist is reacting to more or less commonly known alternatives, namely (in most Western cultures) that there is a single all-perfect, all-knowing, all-powerful, all-good diety. The atheist denies this[1].
The atheist denies more, of course. He denies, roughly speaking, that there are any beings worthy of the term "god". Does this require that he have a clear definition of the term? I think not. I think that there are certain characteristics which distinguish gods from non-gods, among them the ability to act contrary to the laws of physics, their immortality, their emphatically spiritual rather than physical nature. Now, not every purported god possesses every such trait, but there is a more or less common theme.
The atheist isn't committed to the view that there is a well-delineated class of gods, and that he doesn't believe in any of them. It's enough that he knows a god when he (metaphorically) sees one, and that that's the sort of thing he disbelieves.
[1] I am phrasing this in terms of so-called hard atheism, since I don't think the issue arises for soft atheism, sometimes called agnosticism.