I can recall them changing things in the publications long before computerization and CDs, and for reasons other than expounding prophecy. For instance, there was a WT study article that commented on the place in John's gospel where heaven speaks (12:27-30), and the writer stated that the voice occurred to strengthen Jesus. The article directly contradicted what Jesus himself says in v. 30, "This voice did not come for my sake but for yours." This was not some simple error. The stated "application" of the passage was key to the writer's argument in the article. I remember how when this article was "studied" after the public talk, there was present in the congregation a strong sense of unease as the publishers and conductor danced around the WT statement and the scripture's context. When the bound volume came out for that year, the article had been rewritten with no trace of or explanation for the blunder. One would never know what the original article read.
I asked one old Gilead grad I knew about it. He told me that such things were pretty common, and that when he worked in various overseas Bethels, they regularly got paper notices form Brooklyn changing this and that in the publications. One of his collateral duties was to keep a paper file of all these. He said it was remarkable how many of these there were, and they were more than just changes in policy. They were errors in fact. He told me that purging such things in the bound volumes was standard procedure.
After discussing it with him, I came to the conclusion that two basic things were responsible for such blunders. It is not as though the WT writer was thinking, "Let's see how I can pervert the Bible today." Rather the first real reason is that the writers are under pretty severe deadline pressures and so are the proofreaders, so such errors come thru pretty regularly. But the second reason is far more serious and depressing. The official WT view of the Bible is that it is basically a depository of 30,000 or so proverbs, nicely divided into chapter and verse. The common thinking then is that the use of the Bible is mainly to dip into it, pick a verse, and apply it to whatever perceived need there is at hand. That's it. There is rarely, if ever, any attention given to context, in the small or large perspective. That's why the WT writer of that article could "apply" verse 28 the way he did without even thinking of verse 30. If I recall correctly (and that's shaky!), the "need" was something like, "Elders, don't get discouraged. Jehovah will help you out just like he did Jesus when he was down. He even spoke to him from heaven to raise his spirits."
What all this indicates is how poorly Witnesses know their Bibles. Sure, they know certain things like the biblical view of the soul's not being immortal, how to find the book of Daniel quickly, etc. But they are not taught the importance of context, so they just don't know it. They don't even think of it.
For those who might wonder about the ref to this WT study article, I don't have it handy, and looking at the official index and bound volumes won't help since that's all been sanitized. You'd have to get a copy of the original individual WT magazine. I do remember that it was in the mid-late 1980s, prior to 1989. I might be able to find the ref in files ... somewhere ... If someone would remind me, I'll look later.