I'm a fan who only watches the movies, if this has been addressed in a book or comic, please let me know! Thanks

Been watching the prequels again. There are Death Star plans in Episode 2 and construction has started in Episode 3. But in Rogue One, Galen Erso is taken because they're having trouble with some of the engineering. This happens when Jyn is young, maybe 18~ years before the Death Star is fully powered at the end of Rogue One? Sooooo.....I'm guessing the plans created in Episode 2 were problematic, and that's when they captured Galen? Or did they not discover the problem until much later? So did it take 18 years to correct the architecture to make the station fully operational? Or was the architecture finished by Galen pretty quickly and they just kept him prisoner so he wouldn't leak any secrets?