I recall seeing the X rated Clockwork Orange as a child, Rene M gave me the book in 6th grade..
I thought “what is so X about it?”
The answer was the violence. The cold hard violence
“No time for the old in out love, just here to read the meter”
"X" was changed to "NC-17" for no children under 17 due to the porn industry usurping X.
"M" was replaced by PG for parental guidance and PG-13 for parental guidance may not be appropriate for children under age 13.
"G" is still general audience.
"R" is still restricted for teens with parents.
-PJ