Y'all have to remember that the Klingons had possession of the Narada and had held Nero and his crew prisoners for 25 years.
That will give the Klingons plenty of time to figure the Narada access codes and download all the information that they had found.
Also plenty of time for federation spies to steal that same information from the klingons.
The Dreadnought most likely was built from information that was gotten from the Narada. Which mean, that the Dreadnought is not from the future, but is base on future technologies.