I don’t know about USMC but, based in US Army, he might be correct. In the 1970s the Army PT for some units had a possible 500 points. It was based on five events: Situps, Pushups, Horizontal Ladder, 1-mile run, and the Run, Dodge, and Jump. It was later changed to a three event test with 300 possible points: Situps, Pushups, and a 2-mile Run. It would not surprise me if the Marine fitness test went through a similar transition.
You are correct, the change occurred in the mid-70s. My previous response was for the test as conducted in 1971; I have personal memories...