This is by no means a complete discussion of the subject but I will start it with my thoughts and I hope those smarter than me will contribute.
The WT teaches that the changes in doctrine and their understanding of the scriptures over the years is because as we get nearer the end of this system the "light gets brighter" or God allows(?) a better understanding. This is based off the scripture Proverbs 4:18 which states
1 8 But the path of the righteous ones is like the bright light that is getting lighter and lighter until the day is firmly established.
As a witness I never questioned this, but when reading what was written here I now believe that it is dishonest to base this teaching off of this scripture. Especially since the very next verse says
19 The way of the wicked ones is like the gloom; they have not known at what they keep stumbling.
Now wouldn't it be reasonable that mis-interpretations would be likened to stumbling and then those making those wrong interpretations would be likened to the "wicked ones" of verse 19.
You can't take one verse without the other.
Well, that is about all I have on the matter...Now what do the BIG GUNS have