Just got my hands on this bottle a few moments ago and I've watched Sour Grapes too many times. A few things that catch my eye right away is the vintage placement as well as the term Grand Crus above Pommerol. I am not a Petrus historian and I am only using resources available online to compare labels from that year. I've also read that Petrus labels have been inconsistent. So if anyone who has more experience and knowledge wants to chime in please feel free. If this is not the right place for this discussion please delete this post.
A little digging and I found this label shot from a Sotheby's auction back in 2013. While I most certainly defer to those with far superior knowledge on this subject, I hope this may help a little. Link below.
Sotheby's Auction 2013 - Petrus 1949
Good luck. I have served a few Petrus from the second half of the 40's and they were all labelled with the Vandermeuhlen labels. They were always corkage, and there was no risk on my part. It's hard to know if you are actually tasting the real thing. Maureen Downey from the film you mention consults and offers services to help. They may be pricey, but probably not as much as a bottle of Petrus. And if you're selling it in a restaurant just add that to your mark-up. I will say that I have never seen them use the words Grand Cru, only Grand Vin. I have seen Cru Exceptional but have heard that is a sign of a fake bottle.
To help determin if it is authentic or not, i would do the following:
try to access auction catalogs from original owner cellars for label comparison. Acker Live from 4/8/2017 Wolfgang Grunewald colletion has bottle shots of 1945 Petrus, which states "1st des Grands Crus" and has a branded cork. From what I recall, Wolfgang was the original owner for most of his wines
Check if the cork is branded. I don't know general restaurant edicate/policy on this, but I personally would prefer a cut capsule showing me a branded cork, if i was about to purchase a rare and often faked expensive wine! If not branded, the odds are much higher that it is fake. Sometimes top properties did use some unbranded corks on some of their bottles in the past (I have seen it on original owner lafite from the 70s), but I would imagine that with the smaller production of Petrus, this didn't occur as often.
ask the seller about provenance
Examin the fill. While it could be into the neck, it is quite common for authentic older bottles to have lower fills
Apologies for the sideways photo, my computer refused to rotate, but there is a pretty much guaranteed genuine 1945 image for comparison.