There may not have been a formal declaration not to read older publications, but I do remember that when the CD-ROM library came out there was something said about the fact that it went back only to 1950, and that indicated that it might be "confusing" to read older pub's.
The reason this stands out is that I was somewhat offended by that. Here we had a KH library stuffed with books from Millenial Dawn and onward, but we were told not to read them.
The greatest Wt. Theologian Fred Franz who mislead us all with 1975 is now just 'Old Light'
Designs -- Now THAT is funny. I remember when he was idolized as the most indepth and educated speaker at Dist Convs.
Doc
And holy cow, he also had the worst voice for speaking. I heard him at the 1978 International Assembly. Very thin, reedy voice, difficult to listen to. I think he said something then that condemned disco music. Or maybe that was another talk.
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The Odd Life of Jehovah's Witnesses