The overriding identifier is the PLCB code number, which is usually stuck on the bottle somewhere, often right on top of the UPC code. It's a 5 digit number. Once you have that, go to
www.lcb.state.pa.us, click on product search, type in the code and that will tell you what the PLCB
thinks you have.
That's not to say they're flawless... I ran into an inconsistency last summer with Sanford Pinot Noir: A store I visited (and presumably others)had the same vineyard bottling stocked twice on the same shelf about 5 feet apart, with different code numbers and prices for each. Sent an e-mail asking the deal, and I received a reply with an apology and explanation. They then deleted the code number for the cheaper version and reclassified the offending bottles with the other code and thus the higher price. Nice.
For what it's worth, I've enjoyed several vintages of Chateau Souverain's Chardonnay as well as their Winemaker's Reserve Chardonnay, and the reserve was always clearly identified on the label.