Singular "yez"?

[Laurence Horn]

At 11:35 PM -0500 12/12/04, James C Stalker wrote:
>Maybe someday some now young and aspiring linguist will get a really big
>grant to study this issue.  Until that day, I think Wilson is right.  Even
>for professional linguists, language is perception.  When it comes to yall,
>we hear and interpret what our prejudices instruct us to hear.  Clearly
>there are those who firmly believe that heaven does not allow yall as a
>singular, and thosse that believe it does.
>
>Jim Stalker

There is a difference of perception, but there's also an uncertainty
in definition.  What exactly are we counting as singulars?  A number
of posters have brought up cases that push the boundaries of singular
vs. plural.  Take the example I mentioned recently*, which I
originally posted in Nov. 2002--

===========
I was at the pharmacy counter of my health plan a couple of weeks ago
(the only person standing there waiting to pick up a prescription)
and the pharmacist (female, 30-ish, African-American) chastised me
(pointing to the roped-off area a few yards back), "Y'all have to
stand back there".  Definitely a second-person singular "y'all",
although it could be argued that it designated "you and anyone else
(not now present) in your situation".
===========
Is this reckoned a singular by those who dispute the existence of
singular "y'all" and thus a counterexample to the claim, or is this
being taken as an implicit plural?   If the latter, what sort of
example would falsify the claim that y'all cannot be a singular?
This is, I assume, an empirical question, and I'm not someone with a
firm belief (in either heaven or the inherent number-marking of
"y'all").

(*Bethany's example from a Knoxville receptionist is similar,
although I'd think even harder to assimilate to the class of implicit
plurals.)

larry