Brotherhood and Revelations helped "support" the development of ACIII, explains Ubisoft.
Assassin's Creed 3's creative jump wouldn't have been possible without annualising the series, the game's creative director Alex Hutchinson has suggested.
Speaking to Eurogamer, Hutchinson defended Ubisoft's decision to annualise the series, saying that the release of Brotherhood and Revelations helped "support" ACIII's development.
"We have multiple groups now working [on the series]," he explained. "We started this one in January 2010, the same time as Brotherhood and before Revelations.
"The core team on this one has been working at it for almost three years, which is something you can almost never get in the industry these days - it's too expensive, too risky. So we need the other projects to support that kind of development - these big jumps."
Some fans and critics criticised the series' annual releases, with some suggesting that Brotherhood and Revelations were little more than annual cash-ins.
But Hutchinson likens each Assassin's release to a "new IP".
"It's funny, people say it's about how often you release new entries, but I really think it's about how good they are," he added.
"Also, the beauty of Assassin's is that if you do it right it's kind of a new IP. It's still about navigation and combat, but it's a brand new hero, brand new setting, brand new fantasy. It really is as close as you could get to a big budget new IP late in the hardware cycle."