Welcome Gig.
You are hitting on one of the key issues: It isn't what they taught. The issue is that the Governing Body (the self-styled Faithful and and Discreet Slave) sets itself up as prophet/mediator/god for its followers. An earlier thread or two from the last few days dealt with this exact point.
If the GB (I can never use the 'FDS' without thinking of the hygiene product) tells people that the difference is 'new light', they accept it, hook, line, and sinker. By now they are so used to it, that even those that have been around for a while will profess to believe the the WTS never proclaimed 1975 as the end of the world.
Its one thing for JWs to think that the 'light' from the GB has grown brighter, and that understanding is so great now. It is another thing for Witnesses to ignore that their founders believed in things that would make a Jamaican Television Psychic blush. My wife's and my favorite is the Great Pyramid - closely followed by the construction of a home to welcome the resurrected Princes of the earth -Beth Sarim.
If the JWs want to claim to have been on a road with ever-increasing quality of light, then their founders should have had some light back then. Fact is, I don't think there is one belief of Russell's that the WTS would stand behind today - not one. Their Founder had no light.
But these facts are irrelevant to those that accept the WTS edicts as though they are direct statements from God.