Gundam Unicorn takes place in the Universal Century, which is part of the same timeline as the One Year War. 

Essentially, Gundam has numerous timelines/realities/whichever your preferred term is. 

The Universal Century is the 'original' setting, and began with the original Mobile Suit Gundam: 0079, and it's numerous sequels, prequels and side-quels, such as 0083, 08th MS Team, Unicorn, Char's Counterattack, F91, Victory, etc.

Then you also have the Alternate Universe stories, such as Gundam Wing, G-Gundam, Gundam X, Seed & Seed Destiny, Gundam 00, etc. These all take place in their own self-contained universes and timelines, and don't relate to each other, or to the main universe. However, they contain a lot of the same themes and ideas (space colonies, mobile suits, war is a living hell, no-one comes through war unscathed, usually a villain with a mask who is a foil for the hero) as the original Gundam series/setting. 

If you're having ALL mobile suits being mass-produced, you probably need to come up with a reason why they all exist in the same timeline first, and which events have or have not taken place.