For those who prefer stories with an ending, here's how things ended up (although it's a bit like the end of the last episode of the Sopranos).
1. I haven't heard back from LCBO customer service - even though they said I would.
2. I happened to speak to the store manager and the PC today and I filled them in on what the clerk had said to me. This was the first that either of them had heard about it. The store manager was appalled and said he would give the clerk some customer service training.
3. The store manager said that ISTs are actually easier to do now than they were in the past, but when you're requesting a transfer from a larger store it can take longer, because they wait to consolidate all their transfer requests every couple of days.
4. The PC said that she has no idea why the LCBO phone rep told me that the product couldn't be transferred because it was "discontinued". LCBO doesn't even use that term. According to the PC, products are "delisted"... and in fact, ALL Vintages products are, technically speaking, delisted products. (This makes no sense to me, and I'm guessing it's more misinformation. I'm just reporting what I was told.) However, there is nothing to prevent an IST of a delisted product.
5. The PC called the other store this morning and put in a request for my 4 bottles. She received word a few hours later that the 4 bottles I wanted will be shipped tomorrow.
The amount of misinformation and confusion around something so bloody simple is headache-inducing. I'm still not clear on the facts, or what the truth is... or if there IS a singular, definitive truth.