(Films that achieved critical and commercial success were later re-rated R after minor cuts, including Midnight Cowboy and A Clockwork Orange.) The threat of an X rating also encouraged filmmakers to re-edit their films to achieve an R rating; one notable example of this was the 1987 satirical action film Robo Cop, which had to be edited eleven times before it could attain an R rating.

The original X certificate, replacing the H certificate, was issued between 19 by the British Board of Film Censors in the United Kingdom.

For example, the French film Jules and Jim received an X rating in 1962 that was changed to a PG rating in 1991.

In some early cases, films politically motivated received an X rating.

The X certificate was replaced in November 1982 by the 18 certificate.

Sometimes the rating of a film has changed significantly over time.