you forgot to add for 1960. How many people would name their daughter Brenda or Connie or Janice or Rhonda? Or their son Douglas, Dennis or Raymond? As for Madison, I'll give you that the rise in use for a girl's name was triggered by Splash, but your assertion that it wasn't a name at all is incorrect.
Wikipedia: As a masculine given name, Madison can be found within the top 1,000 names for boys in the United States up until about 1952. Madison returned to the top 1,000 ranked names for boys in 1987, remaining there through 1999, and it also was the 858th-most-common name for boys in 2004, but it remains uncommon as a masculine given name.[3]
Even one of Thomas Jefferson's bastard sons was named Madison.