Possible Clues:

• Flower Power era
• The swinging decade
• Era between the fifties and seventies
• The number of knots that came years ago?
• Nine in where the pigs are years ago
• Team's mounting efforts to knock off runs - time to retire?
• Hippie decade
• Hippie era, with 'The'
• Decade when ZIP codes were introduced
• 'Flower Power' era