In the "Gala" scene where they are examining the pictures, they spot the picture of John and Yelena Davis. The picture plaque visually shows "2008" as Holly reads out loud "1988."
When Holly takes the picture at the train station of herself and Greg, they show the selfie throughout and Holly is pursing her lips. Later however, when she looks at her phone to delete the picture, she has a broad smile in the photo.
The posters for the Christmas excursion train state it is on the "Long Island Railroad", which the actors repeatedly refer to as the "Long Island Railway." The carrier's actual name is the "Long Island Rail Road"---two words.
The mystery charm, which was supposedly made in the 1980s, shows the Manhattan skyline looking south toward the Empire State Building which they verified by holding the charm and comparing it to the actual view. The Manhattan skyline in the 1980s, and therefore the charm, would have included the twin towers of the World Trade Center.
The Long Island Rail Road's 2019 Holiday Special was pulled, not by a steam engine, but by LIRR #510, an EMD DE30AC dual-mode (diesel-electric or third-rail electric) locomotive. The railroad was one of the first to convert to diesel and hasn't had an operational steam locomotive since 1955. The locomotive shown in the film was Canadian Pacific Railway #2860, a Royal Hudson, currently on static display in Squamish, British Columbia.
The steam locomotive pulling the Long Island Rail Road Christmas excursion train is Canadian Pacific #2860, a Royal Hudson locomotive that operates between Vancouver and Squamish in British Columbia---nowhere near New York.
Throughout the film, they emphasize the Christmas tree charm worth $3,000; however, an at the end of the film, it is the only charm they don't even mention, so the viewers never find out what it represented.