There had to be something that caused this change.
Back in the late 80s there was a local Dentist in our area who was dying and volunteered to be the first recipient of a mechanical heart. He lived for a time afterward and showed the full range of human emotions.
This, coupled with all the heart transplants that became commonplace afterward, the JW notion that the heart was something more than a pump, was blown to shreds.
True to form, they never owned up to the misinformation they had spread all over the world. Instead, they just stopped talking about it until it just went away.
But it didn’t go away.... lots of us remember.