well the thing here is that they really have little idea happened in the past as wars almost wiped out the human race if you look at star trek the next generation they barely knew who Zefram Cochrane was people from the 1980's good luck remember just because they gave him the formula makes him the original inventor of it once Scotty gave him the formula their minds would have interpreted the chain as it now is not as it was with out something to block the change in the time line they are subject to the history as it is not as it was so Scotty may have been right the first time and then right afterwards as well

Well, the thing here is that they really have little idea happened in the past, as wars almost wiped out the human race. If you look at Star Trek: the Next Generation, they barely knew who Zefram Cochrane was. People from the 1980's, good luck!

Remember, just because they gave him the formula makes him the original inventor of it. Once Scotty gave him the formula their minds would have interpreted the chain as it now is, not as it was. Without something to block the change in the timeline, they are subject to the history as it is, not as it was, so Scotty may have been right the first time and then right afterwards as well.