You are correct it is 4 years on vehicle transfers within California. This is from BAR's site.
SMOG CHECK REQUIREMENTS
1 Includes gasoline, flex fuel, hybrid, dedicated propane, and natural gas vehicles. A Smog Check is required for all out-of-state 1976 model-year and newer vehicles registering in California for the
first time and other initial registration events determined by the Department of Motor Vehicles.
2 Vehicles four model-years and newer are not subject to biennial (every other year) or change-of-ownership Smog Checks. Add four to the model-year of a vehicle to determine the first year a vehicle will be subject to a
change-of-ownership Smog Check. For example, a 2010 model-year vehicle will be first subject a change-of-ownership Smog Check in 2014 (2010+4=2014).
3 Fifth and sixth model-year vehicles are not subject to biennial Smog Checks. However, a change-of-ownership Smog Check is required. Add six to the model-year of a vehicle to determine the first year a vehicle will be
subject to a biennial Smog Check. For example, a 2010 model-year vehicle will be first subject to a biennial Smog Check in 2016 (2010+6=2016).
4 In the future, BAR may identify some vehicles that have GVWR of 14,000 and less or that have problematic OBD II systems that may require the BAR-97 test.
5 Fleet vehicles are subject to the ARB Periodic Smoke Inspection Program (PSIP).
Legislation enacted during 2004 made several changes in motor vehicle Smog Check exemptions that became effective in 2005. Following is a summary of the revisions and the effective date of each change.
Beginning January 1, 2005, vehicles six or less model years old are exempt from the biennial Smog Check inspection requirement. For vehicles with registration renewals due in the 2015 calendar year, this exemption includes model years 2010, 2011, 2012, 2013, 2014 and 2015.
Beginning January 1, 2005, vehicles four or less model years old are exempt from the Smog Check inspection requirement upon change of ownership and transfer of title transactions with DMV. In 2015, this exemption includes model years 2012, 2013, 2014, and 2015.
Beginning April 1, 2005, the 30-year rolling exemption is repealed. Instead, vehicles 1975 model year and older are exempt. Therefore, 1976 model year and newer vehicles will continue to be subject to biennial inspection indefinitely.
Beginning April 1, 2005, a vehicle being initially registered in California that was previously registered in another state will be exempt if it is a 1975 or older model year vehicle. Newer vehicles, including the newest six model years, are not exempted and are required to undergo a Smog Check Inspection upon initial registration in California.
Beginning January 1, 2010, all 1998 and newer model year diesel vehicles with a GVWR of 14,000 pounds or less are subject to Smog Check inspections.
JUsta, its just a wrench thrown into our program just like the odometer on the bar-97 if the mileage is too low you get a red screen with something like "the mileage is too low ! call service asap ! " but you stick a diesel in it and it lets you do it , so BAR can collect money off us . but yes... we are the screw-ups and bottom feeders . so bar has spoken it .