Not true.
June 13 to July 11, 2012: Birth of Draco event (No Ncoin needed)
This, one day before July 4th:
June 12 to July 3, 2013: Angel Cat Letter Collector event (No Ncoin needed)
Continued:
June 25 to July 9, 2014: Fortune Teller event (No Ncoin needed)
June 24 to July 8, 2015: Watermelon Smash event (No Ncoin needed)
These two weren't on July 4th but pretty damn close:
June 15 to June 29, 2016: Red Libra event (No Ncoin needed)
July 20 to August 10, 2016: Chef Monkey event (No Ncoin needed)
Continued:
June 28 to July 19, 2017: Red Libra event (No Ncoin needed)
June 20 to July 18, 2018: Red Libra event & 50% - 300% Exp Boost (No Ncoin needed)
June 12 to July 10, 2019: 15th Anniversary - The Ultimate Celebration event (No Ncoin needed)