Unless I interpreted this wrong, I think I may have the answer, though I'm not entirely sure.
If someone has already registered in the lowercase form, then if you changed the uppercase account to lowercase, then it would be the same name as the lowercase account. And if someone has already registered in lowercase, that should answer your question as to the captial letters's difference in your second to last post, as say we had two 'Drew's. drew, and Drew, if both registered, would prove that capital's make a difference in names.
But, I can sign in without capitalizing my name, so I guess in the end I couldn't answer your first question, but I'm positive two people can't have the same name, therefore your second question is hopefully answered. If this isn't allowed because it's not entirely on-topic, tell me and I'll delete it.