Oh, yes, I can remember when they launched the six-month BS program.
It must've been early 1969 or late 1968 that "the six-month home bible-study program" was mandated. (The library CD only goes back to 1970 so we have to use a bit of extrapolation)
*** Kingdom Ministry 3/70 p. 4 pars. 4-5 Presenting the Good News—Become ‘Intensely Occupied with the Word’ ***
"A little over a year ago we were introduced to the six-month home Bible-study program. We immediately grasped that this would be an additional effective method to help get the work done in the short time remaining.
5 Now reports from the field show that Bible studies are being discontinued as publishers realize that the student is not making progress. This is entirely proper. There is no reason to spend our time with those who obviously are not really interested in doing something about the truths they are learning."
Remember, that's more than 50 years ago because of "the short time remaining".