No. As far as I can tell, singular "y'all", when it exists, is an implied plural. What you might hear as singular "y'all" is, say, when you go into a restaurant and say "do y'all have Coke?" to the server - that doesn't refer to just the server but to the restaurant as a whole. But I'm not a linguist and also I don't spend much time among people with heavier Southern dialect, so you shouldn't believe what I say.

No, you've got it right. A lot of people trying to be cute and make southern language seem more alien than it is are over-"correcting."

When southern people say y'all to one person, they're really addressing you and your family (even though you might be the only one there.) If I ask "how y'all doing?" I want to know how you and yours are doing.