TRIVIA Question - Number of spike pins allowed

Up until the late 80’s or early 90’s, track events allowed 6 pins on each shoe. The 7th pin must be a stud.

Depending on your race, you had to choose wisely where to put that stud.

Today, you can buy spikes with 8 holes and fill them up… it’s the spike length that gets checked at the control room.

Does anyone know when that rule was changed?