Catalytic converter and engine type

I have a 2000 Subaru Outback and live in California.  In 2010, I had some engine trouble that damaged the catalytic converters.  My mechanic repaired both the engine and the catalytic converters in 2010.

Recently, in 2014, my car failed a smog check because the catalytic converters did not match the engine type.  I talked to my mechanic about this and he explained that the catalytic converters he installed in 2010 were legally acceptable, but the California standards have changed so that the same converters that were acceptable in 2010
are not acceptable in 2014.

Is this a reasonable explanation?  Or is this a problem that could have been avoided?