Code of the Lifemaker was created in 1983.
Found it on BookSleuth, turns out it was written in the 80s, 'Code of the Lifemaker', and it was on Titan, not Mars. Mars was a cover story.
Speak in Code was created on 2012-04-24.
The Code of the Harpers was created in 1993.
Code Revivial was created in 2004.
Secrets of the Code was created in 2006.
Code to Zero was created in 2000.
Norse Code was created in 2009.
The Tic Code was created in 1999.
QR code was created in 1994.
Code of the Krillitanes was created in 2010.
The Code of Life was created in 2001.
Code of Rubrics was created in 1960.