The suit rule only applies to the Public talk, and Memorial, not sure if the letter said Memorial or not! But I well remember that the letter spelled out "Public Talk". In the congregation I was in, we went over that letter in a ms & elder meeting. I still can hear head jerk elder saying "We can all read between the lines here, what the gb is really saying, is all brothers on the platform myst wear suits! " and that stuck for year's!
Dwain