I never doubted it...not for a minute. Until this year.
I now realise I've learnt more about the religion this year than I ever knew before. I was one of those than went blindly along with everything. I had total trust in the GB that they were doing the research for us and we could rely on them 100%
In hindsight, it was lazy. I couldn't be bothered to check for myself, but then why should I?
I think most people I know believe what the GB tell them. A few may have niggling doubts but have a 'well, I don't really believe that but I'll go along with it for now' attitude.
One thing I do know, is a lot of JWs today seem to have very little bible knowledge. When my husband was talking to the COBE the other day, he said he was shocked at how little the COBE knew. They are so busy getting in the hours, I don't think they study deeply. I didn't. I just studied WT material and accepted it as fact.