The example of "Sambo" as an African-American racial epithet illustrates well how connotation shifts over time.   The original Sambo stories were about a child in INDIA, not in or from Africa (hence the tigers).   
Try telling that to an African-American audience today, though, if you were to read the "Li'l Black Sambo" stories to a preschool class.
Perceptions and meanings change over time.