Tom Anderson is involved in the large multi-vehicle collision caused by Beavis and Butthead falling out of the trunk of Dusty's car on the highway near Washington, DC, and does significant damage to the front end of his SUV. In later scenes at the White House, however (supposedly later the same day), his vehicle is undamaged.
The writing on the side of the Dream America bus changes throughout the film. When Beavis and Butt-Head go down to board the bus, the font has changed from when we first see the bus from Dallas' window. Also, later in the film when the boys rejoin the bus, the name of the tour company is now spelled as "DreamAmerica" with no space.
When the duo are on the plane to Las Vegas, the people sitting in the row immediately behind them changes - most easily seen as the man sitting on the aisle seat changing from a man in a vest (who later asks if there is corn in the dinner from another row on the opposite side of the plane) to a man in a business suit
There are a number of inaccuracies with the airport when Beavis and Butt-Head land in Vegas. There is only one major airport that receives jet airliners in the city, which is McCarran International Airport. The actual airport has a number of slot/gaming machines in the terminals. Furthermore, the view from the windows is inaccurate. The airport is surrounded by office buildings to the east, large multi-story office/business plazas to the south, freeway to the west, and housing to the north.
As the airplane takes off for Las Vegas, one of the runways is number "41". Runways are numbered by their magnetic headings, and thus the highest runway number possible is 36 (360 degrees, meaning north).
The front entrance of the Old Faithful Inn does not face Old Faithful. As viewed from the front, the geyser is situated approximately 90 degrees to the left. In addition, the entrance has a large canopy covering the loading and unloading of passengers.