I personally don’t think it’s as simple as looking at restaurant wine lists. Here is why I think that (though I may be mistaken).
Here’s what the Perrin family says about Beaucastel Blanc VV:
“Considered as one of the greatest white wines in France, only 6000 bottles of this wine are produced. It’s made with 100% very old Roussanne vines and harvested slightly over ripe. This exceptional wine must be drunk within 3 years or after 15 years. To be enjoyed with gastronomic cuisine.”
Whichever vintage you click on it seems to say this, so I think it’s general advice vs one vintage being an outlier. But don’t take my word for it, see: Château de Beaucastel Châteauneuf-du-Pape Blanc Roussanne
So if the Perrin family are right, you should drink the 2018 or younger. Or the 2006 or older. Or let’s give or take a year in case they don’t mean from the vintage year etc.
Still, here are the vintages on the Oustalet restaurant’s wine list, if I read it right:
Plainly, and whichever way you look at it, there’s a discrepancy between what the Perrin family say on the website for Beaucastel, and what’s offered in the Oustalet restaurant.
Of course there’s the risk of a category error here. Are we talking about the best times to drink a wine, or times when wines are enjoyable (if not at their best).
My view is that wines on restaurant lists are often there way outside their optimal drinking windows, and this makes sense to me, in a way, because:
storing wine ties up capital and many restaurants aren’t in the same hands for decades and need cash flow
restaurants sell what people want to buy (at the less wine geek end people may want to drink Beaucastel CNDP at Oustalet but not shell out hundreds of euros for an old one; at the more wine geek end someone may have stored a case at home and want to check in on it without taking the case from storage, or with friends create a mini-vertical - you do get groups of very wealthy wine geeks at such restaurants)
aged wines in restaurants are very expensive (as Oustalet’s excellent list shows)
in such a place, the list perhaps shows what’s available but there ought to be a sommelier and their advice is likely to be to drink some vintages not others - in that list you’re not seeing the sommelier’s advice
I’d be wary of opening wines because said vintage is available on a restaurant list.
Incidentally, I haven’t and can’t justify the time going through Oustalet’s list, but the sense I got was that if you look at the non-Perrin wines, the youngest wine is generally older vs its expected drink window. And I wonder if that’s because they pride themselves in offering a particularly wide range of Perrin wines - as you might expect.
BTW, it’s also the case that restaurants get cleared out of old wines. The best list in that region is probably at Beaugraviere in very down-at-heel Mondragon. Visits by wine enthusiasts have cleared out much of the old Ryas. What is offered is what’s left. Though I should say, it’s still a remarkable wine list. If you can visit, do. It’s expected to close soon (and you can Google about it). I think Nick Lander or his wife Jancis wrote about it fairly recently.
But if you look at Auberge Montfleurie, an excellent restaurant not that far away, they have a great wine list. I had a 2013 Dom des Accoles Mioncene which I’d never come across and was wonderful. But even such a brilliant restaurant doesn’t have N Rhones from, say, 1999 as they almost certainly weren’t in business then and wouldn’t be able to tie up lots of capital like that. Also they probably have a different clientele to Oustalet.
Again, if you look at places selling Gonon in that part of the world (at cellar door plus modest markup) it’s young. But of course… It all gets drunk! It’s not that they think it’s at its best then! Just none survives. Often the available whites are older. That’s supply and demand, not a particular comment on windows, I think.
That’s my experience and humble opinion. Well chosen restaurant wine lists can, especially at the lower end, point one to gems (incidentally the house white at Beaugraviere three years ago was from Dom Ste Anne). But I’d be very wary of using them as a proxy for drinking window advice. For that, I’d ask the wine maker or, if in the restaurant, the sommelier. But each to their own.