The plugin doesn't create or add users to blogs, only the blogs(active) a user is already a member of show in the dropdown. The same blogs that would show on their "My Sites" page should show in the dropdown.
So, in a) that would be normal if the user's primary is blog 1. The main blog appears on their "My Sites" page as their primary. (Not sure why the spammer without a blog is still listed there - that is a bug)
In b) a "spam" user has no active blog, so you are unable to switch the primary, also normal behaviour. Unspam the user, and you'll be able to switch amongst his blogs(depends on how many blogs he belongs to) as primary. Now, even though a user is "Spam" at SuperAdmin->Users, the blogs listed there beside their name should also be inactive, therefore their primary blogswitcher should also be empty.
In c) if a user only has one blog, the main, that is all that will be listed. Add them to some blogs, then visit the switcher once again. (or enable Dashboard blog, or Tags blog using Donncha's plugin at SuperAdmin->Options)
Those pics all look normal to me.