And so the search for missing pronouns goes on.

You know, English has not been logical in its treatment of pronouns. In Chaucer's time, "hir" did the job of "his", "hers" and "its". I've read that nobody even knows where "she" came from. And we still don't have an accepted pronoun for you-plural.

Thus (as y'all have mentioned) we have

you (unclear)
y'all
all y'all
y'uns
you guys
youse guys

In my opinion, people who sneer at these usages are snobs who don't really understand their own language - and its shortcomings.

But to get back to the Texas lawman of the song, I'm getting more and more convinced that he is addressed as "y'all" because he's a lawman, and "y'all" here is trying to convey the formal. It's like the situation with the Texas supervisor and the diver. The supervisor addressed the diver, who was not a personal friend, as "y'all" because it was a more formal usage.

I know there were many Germans in Texas once, and in German the formal you (Sie) is plural, whether or not one or more persons are being addressed. This concept (plural = formal) might have hung on.