There are a great many reasons it becomes difficult to "prove" to active JW's that the Watchtower Society has had an amazing series of CRACKPOT teachings, beliefs and assertions over the years.
First off, the availability of old publications is problematic. The Society has cleverly sucked them out of the libraries of local Kingdom halls. Older Collectors are often dead or apostate.
Ebay can provide steep asking-prices.
But--a few years back, I discovered the availability of REPRINTS in quality self-published form on LULU.com and Amazon.
These reprints are beautifully done and easier to read than an old, moth-eaten, mildew-stained yellowy tome from the early era!
Here are a few of the titles now available at extremely reasonable prices:
"Millions" book - http://www.lulu.com/content/paperback-book/millions-now-living-will-never-die/116824
"Millions" e-book - http://www.lulu.com/content/e-book/millions-now-living-will-never-die/8214548
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"Desolations of the Sanctuary" book - http://www.lulu.com/content/paperback-book/the-desolations-of-the-sanctuary/8034794
"Desolations of the Sanctuary" e-book - http://www.lulu.com/content/e-book/the-desolations-of-the-sanctuary/8243356
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"Demonism and the Watch Tower" book - http://www.lulu.com/content/paperback-book/demonism-and-the-watch-tower/7790259
"Demonism and the Watch Tower" e-book - http://www.lulu.com/content/e-book/demonism-and-the-watch-tower/8215067
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"Home and Happiness" book - http://www.lulu.com/content/paperback-book/home-and-happiness/6120424
"Home and Happiness" e-book - http://www.lulu.com/content/e-book/home-and-happiness/8215367
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"Our Lord's Return" book - http://www.lulu.com/content/paperback-book/our-lords-return/1431553
"Our Lord's Return" e-book - http://www.lulu.com/content/e-book/our-lords-return/8215677
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"A Bible for the Scientist" book - http://www.lulu.com/content/paperback-book/a-bible-for-the-scientist/143371
"A Bible for the Scientist" e-book - http://www.lulu.com/content/e-book/a-bible-for-the-scientist/8214925
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"The Way to Paradise" book - http://www.lulu.com/content/paperback-book/the-way-to-paradise/185257
"The Way to Paradise" e-book - http://www.lulu.com/content/e-book/the-way-to-paradise/8215251
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"A People For His Name" book - http://www.lulu.com/product/paperback/a-people-for-his-name-a-history-of-jehovah%e2%80%99s-witnesses-and-an-evaluation/712752
"A People For His Name" e-book - http://www.lulu.com/product/e-book/a-people-for-his-name/6328691