Seems that on Saturday, after I made the phone call, I got a voice mail at home from Ruth, the store manager at the store I had the problem with. Left a message, following up from the call earlier that day.
Problem was, though that this was while I was still at work. No biggie, call back. So I did on Sunday, and found out ultimately that she's at a manager's convention in Las Vegas. No problem.
I figured that the best way then to contact somebody about this is to contact the toll free number again and explain this, which will get a message to the owner of the franchise. Did so this morning, much to my success.
Ultimately, I spoke with somebody named Dennis. No relation. =)
We chatted a bit, and when we got down to business, I relayed a summary of my story. What struck us as interesting was that Pablo's story (as passed to Dennis by Ruth) didn't jive with mine. His story was that he never interacted with me, and in fact I had my information relayed via the drive through attendant. (I thought this particularly funny, as I have never carried a driver's license, ergo I have no business in the drive through.)
He then noted the coupon, which not only was he looking at a copy of (there was a hint that it might have been the very one I presented), but he concurred with my observations of "any size", and likewise concurred with my opinion that if it says "any size", there should be no such restrictions as Pablo had outlined on Saturday. We also agreed that the current circumstances were particularly ironic (kudos to beccak1961 and usagiweaver for that pointer), and as nice as the company tries to be, there are limits on how these coupons are handed out - and they're usually done so for situations such as this. (There are other coupons for, say, a free hamburger that are given to kids, but that's a different ballgame there.)
The long and the short of it was that he was very apologetic (as can be expected), and he's sending out coupons. He indicated there were also previous problems with Pablo, so maybe this is an ongoing issue thing - which sucks, but I'd rather they know something is amiss than have it continually go amiss and have them lose business.