Just because religions go through major institutional changes, since they are in fact very human at their core, you have to give some credit to the fact we are still talking about Buddha, Jesus and Muhammad.

At least, the Torah has survived with minimal change.

Well we don’t have the autographs for any holy text past a certain point, so I’m not sure that’s true. But with faith it doesn’t matter.

We have physical copies of older versions. Just because it's religion, doesn't mean it's made up.

The Dead Sea scrolls can be compared to the “oral” tradition (mostly actually written) to see how far it shifted.