In which year did WIPO become a specialized agency of the United Nations system?

WIPO's summary of its Convention states that WIPO "became in 1974 one of the specialized agencies of the United Nations system", and the Agreement between the United Nations and WIPO entered into force on 17 December 1974. The year 1967 is when the WIPO Convention was signed at Stockholm, and 1970 is when it entered into force. The year 1996 is when the WCT and WPPT were concluded.