So what date in 1992 did the emission regs change?
Yup, 1st August 1992 made test more stringent and 1st August 1996 introduced the advanced test for passenger vehicles with advanced control systems such as
3 way catalytic converters. There was a "transition" period between 1st Aug 1992 and 1st August 1995 for some vehicles which were not built to conform with EC standards.