We all know that the Death Star's original design was done by the Geonosians. The people who made the plans did not want them to fall under the control of the Jedi or the Republic, so their ally Count Dooku took them away to a safe location.
Needless to say it had changed hands more than a few times by the time of Rogue One.
Spoilers for Rogue One:
In the movie Rogue One, the Death Star blew up the archive on Scarif with the Death Star's plans still plugged into the Citadel's transmitter. Galen Erso had said, "I know there's a complete engineering archive in the data vault at the Citadel Tower on Scarif." Could the Empire really have blown up the only complete plans in existence, leaving them with no copy?
It is clear from the events of Star Wars: A New Hope that the Empire never managed to get the "stolen Death Star" plans back from the Rebel Alliance.
To make thing more complicated, the Empire eventually managed to fix the flaw in the reactor in time for the second Death Star. To do that without the complete plans would have been painful.
So I was wondering: did they have backups of the plans for the first Death Star?