(at around 6 mins) The bedspread early on changed from white with blue stripes to completely white.
Steve's car keeps changing between a Mk V VW Golf and a Mk VI.
Billboards advertising the three teens missing show a number with the 480 area code in it. The film takes place in 1997, but 480 area code was not created until 1999.
(at around 17 mins) The video portions of this film are set in March of 1997. At one point, Ashley says how much she loved the movie Contact (1997); however, that film didn't open until July, roughly three months after the events of the film took place.
When Josh first "interviews" Ashley in a parking lot, a 2002 Nissan Altima is visible in the bottom right corner, despite the scene taking place in 1997.
(at around 10 mins) When Josh is first filming his reflection and asks a pedestrian to get an interview, but is declined; latter-day vehicles can be seen driving around in the background - despite the film taking place in 1997.
A green energy car is visible on the freeway as the trio journey to find the Phoenix Lights.
The car radio stations are in the Los Angeles area.