In those languages that use "Chinese characters", simplifications have been made. First by Japan in 1947, then by the People's Republic of China in 1956, 1964, and 1986. In each case there were instances where a traditional character's new simplified form coincided with a pre-existing traditional form. This means that one writing system might see two variants of one character where another writing system sees two distinct characters.
If you can think of a more concise title for this category which is still descriptive, please improve it!