One of the delights of moving to The South is discovering
that "y'all" is really singular ... "all y'all" is plural.
Who knew?
True southerners are born knowing this. I came from California, so it took me awhile to catch on.
Well, both are plural...it’s just that “y’all” can be a subset of “all y’all”, in which case it really means “summa y’all”. So you have to add the “all” in there to be clear that you mean the whole group.
By the way, I knew a guy from the Midwest — I can’t remember where — who used “yins” to indicate the plural “you”. I had heard “yous” and “you guys” from non-Southerners before, but that one was a new one on me.