I was active after 1987. It seems that they were in a long spell of not changing the doctrine too much up until 1995.
So my guess would be that there were some "safe years" inbetween there somewhere, but by "safe," I mean that they didn't do ANY doctrinal changing.
My guess would be that there were several periods just the same way along their entire existence- periods of no new light and doctrinal changes.
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In 1995 the teaching on the GENERATION went into effect which made ERROR out of all previous teaching all the way back to 1916.
As JW Facts website tells it:
"When this was changed in 1995 with an article explaining that a generation could extend for multiple lifetimes, many Witnesses saw this as indication the Governing Body had lost faith, no longer confident that Armageddon is close at hand. Since 1995, the growth rate of Jehovah’s Witnesses has fallen dramatically. In 2010 the teaching changed back to say that it will be within 2 overlapping lifetimes, so it will be interesting to see if this can be used to try to turn around the declining growth rates."______________
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So everything before 2010 was "adjusted" making 1995 an ERROR to be adjusted as well.
Boom goes the dynamite.
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These people are O.C.D. compulsive about tweaking every little jot and tiddle and cannot help but meddle.
I had an old friend JW who said to me, "You know only the Society admits when they are wrong."
I answered, "Two things about that statement need to be faced. First, admitting you've been wrong actually means you've been WRONG; so there goes the accuracy of calling it the TRUTH. Secondly, Other religion actually know what they believe--so, there is no reason to change it or admit it was wrong."