"If You Do n't Know Me by Now" is a song written by Kenny Gamble and Leon Huff, and recorded by the Philly soul musical group Harold Melvin & the Blue Notes. It became their first hit after being released as a single in 1972, topping the US R&B chart and peaking at number three on the US Pop chart.

Based on this passage, when did if you don't know me by now come out? Let's give stream of consciousness first:
To answer the question, consider the following: It became their first hit after being released as a single in 1972, topping the US R&B chart and peaking at number three on the US Pop chart.
So, the final answer is 1972.