Mary is shown tucking Chuck into bed in 1994 and he is obviously 9 or 10 years old. However, since Chuck started school at Stanford in the fall of 1999, he should have been 12 or 13 in 1994.
In the season 3 final, Chuck and his sister as children are seen talking to their dad in 1991 about a bracelet (or necklace) that Chuck broke. We then see Chuck and Ellie as adults, remembering that same day and Chuck saying something like he used to think that was the reason his mom left a few days later. In the season 4 opener, Chuck is being tucked into bed looking the same age he did in the season 3 final flashback (1991), but the date in the season 4 opener is 1994. Though they do stick with saying his mom disappeared 20 years ago, so the date his mom is reading and tucking him in should be 1991.
Near the beginning, when Chuck is kissing Sarah, his hands are on her hips but in the close-up they are on her face.
Casey says it is time to deploy the best communist weapon made, the AK-47, which fires 7.62x39 ammo. However, what he is holding is an AKS-74U "Krinkov", which is a much newer, shortened assault rifle in 5.45x39.
When Chuck and Morgan are entering the Volkoff Industries headquarters in Moscow, a statue of a woman with a sword is briefly glimpsed. This statue exists in real life - it is called "The Motherland Calls" and is actually located on the Mamayev Kurgan, a hill in Volgograd (perhaps better known as Stalingrad) - a city very far from Moscow. The statue is over 270 feet in height and was erected to commemorate the Battle of Stalingrad.
Chuck and Morgan's flight to Moscow is shown on a flight path which is a very nearly straight line between L. A. and Moscow on a flat, Mercator Projection map. However, the world is a sphere. The path of a real flight from L.A. to Moscow would, on a flat map, appear to leave L.A. almost due north, arch west of Hudson Bay, over northern Greenland, and curve down to Moscow.
The map of Europe shown is totally wrong: Austria is shown where the Czech Republic actually is and the Czech Republic is shown where Slovakia actually is.