Yes, but it's obvious KH1 didn't take just a year. And it's obvious KH2 didn't just take 2 years. If you look at the time they actually started developing the games themselves, assuming they did so a short while after each game was announced, then it would be 4 years development time. Which is honestly pretty standard for a lot of video games.
Plus, KH3 JUST started development. That is obvious. This isn't a case where KH3 has really been developed since 2010 (Yeah, IGN quit pulling that bullcrap, the Osaka Team went on to make KH3D after BBS, they COULDN'T have been working on KH3 all this time >_>), this is a case where they have had maybe a couple months at the most.
People usually get confused with the whole ''development'' word. I am certainly not an expert but it does consist of two very different things: pre production and production. With a game like Kingdom Hearts 3 it certainly is more than possible that it has been in low profile pre production since 2010 or even longer since it has been a concept that is alive for a very long time. Now it probably didn't start for real before 2012 but it certainly has been on works for a while.
Then there is the production stage and this is what probably has just started recently. Late 2012-early 2013. So pretty much the development of the game is full speed ahead. Now you are saying that it would take 4 years to develop the game. I'll respond that I don't believe that. If all goes well with Osaka team on HD development I suspect the development would take around 2,5-3,5 years. I think the japanese release of KH3 will be late 2015 or early 2016.
None of the KH game main development phase has taken 4 years, believe me. For KH1 I don't know when PS2 development kits were out but it couldn't have been more than 3 years max. According to wikipedia it started as late as february 2000 and that is quite believeable date, the source is japanese so I won't go further with that. Let's say that date refers to the start of the main development, it would mean almost exactly 2 year development cycle.
Kingdom Hearts 2 then. According to Nomura:
Dengeki PlayStation magazine: When did the plans for Kingdom Hearts II come up?
Tetsuya Nomura: The plans were around since the time when Kingdom Hearts: Final Mix, wrapped production, but the specifics weren't decided until this July or August.
So let's speculate the main development started in July 2003. That would make it 2,5 year main development cycle. Tho even that quote is a little strange. ''Plans'' almost sound like more pre production than production stage so it might be less than that.
Birth By Sleep then. Now again the sources from Wikipedia are Ultimania and Famitsu so I cannot state for the accuracy since I do not read japanese. However according to them:
Development of the game began in June 2005 and was originally intended for the PS2 with Sora as the prototype protagonist of the game.
Development of the game began before the release of Kingdom Hearts II Final Mix+. The plot was completed, but development was halted six months after it began due to development of Re:Chain of Memories. The development team changed the platform to the PSP so as to make use of the PSP's functions such as co-operative and competitive multiplayer gameplay.
This is the hardest one of all to calculate since the game both changed the platform and the whole premise. So June 2005-January 2010. And at late 2005/early 2006 the development comes to a halt and development on Re:CoM begins. This is where things get hazy because we don't know exact dates but let's say that Re:CoM took them little over 1 year to develop or at least that is the time that BBS was completely on halt.
So in the span of around 3,5 years or probably even less they developed BBS and they did it while doing major revisions to the project like changing platform from PS2 to PSP and changing the whole story.
