@lxo Good suggestion to check the Bulletin!
Issue 1 (Feb 1986) through Issue 20 (Jan 1996) have a definition with just "two specific freedoms". In Issue 21 (July 1996) that became "three specific freedoms". It remained 3 freedoms through the final issue, Issue 24 (Mar 1998).
https://www.gnu.org/bulletins/bull20.html
https://www.gnu.org/bulletins/bull21.html
https://www.gnu.org/bulletins/bull24.html