That reading of DA letters must have been before my time or a peculiar practice by individual congregations. I started going to meetings in the early 50's at an age to remember.
I can remember it being announced that someone had returned to "Christendom" and some weeks later a talk being given about it being an act of disassociation. I can remember being warned to throw out "apostate" literature and not accepting another religion's publications. I can also remember being told how to act if approached by "apostates" when coming to and from assemblies/conventions. I can also remember being warned not to watch religious programs on TV or listen to the radio.
For the most part they avoided calling attention to any individuals or groups not wanting to make people curious and investigate secretly.
Blondie